diff --git "a/\354\235\264\354\235\200\354\264\235/week5/backjonn_3613.cpp" "b/\354\235\264\354\235\200\354\264\235/week5/backjonn_3613.cpp"
new file mode 100644
index 0000000..5e24b57
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week5/backjonn_3613.cpp"
@@ -0,0 +1,102 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MOD 100000
+#define MAX 100010
+//this is not for development, but for PS.
+//this line is super critical for development.
+
+using namespace std;
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    string s;
+    cin >> s;
+
+    if (s.empty()) {
+        cout << "Error!";
+        return;
+    }
+    
+    if ('A' <= s[0] && s[0] <= 'Z') {
+        cout << "Error!";
+        return;
+    }
+
+    bool has_underscore = false;
+    bool has_uppercase = false;
+
+    for (char c : s) {
+        if (c == '_') has_underscore = true;
+        if (c >= 'A' && c <= 'Z') has_uppercase = true;
+    }
+
+    if (has_underscore && has_uppercase) {
+        cout << "Error!";
+        return;
+    }
+
+    if (has_underscore) {
+        if (s[0] == '_' || s.back() == '_') {
+            cout << "Error!";
+            return;
+        }
+        for (int i = 0; i + 1 < s.size(); ++i) {
+            if (s[i] == '_' && s[i + 1] == '_') {
+                cout << "Error!";
+                return;
+            }
+        }
+
+        string java_style = "";
+        bool capitalize_next = false;
+        for (char c : s) {
+            if (c == '_') {
+                capitalize_next = true;
+            } else {
+                if (capitalize_next) {
+                    java_style += (c - ('a' - 'A'));
+                    capitalize_next = false;
+                } else {
+                    java_style += c;
+                }
+            }
+        }
+        cout << java_style;
+    } else {
+        string cpp_style = "";
+        for (char c : s) {
+            if (c >= 'A' && c <= 'Z') {
+                cpp_style += '_';
+                cpp_style += (c + ('a' - 'A'));
+            } else {
+                cpp_style += c;
+            }
+        }
+        cout << cpp_style;
+    }
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week5/backjoon_1564.cpp" "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1564.cpp"
new file mode 100644
index 0000000..e8a229e
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1564.cpp"
@@ -0,0 +1,78 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MOD 100000
+#define MAX 10000
+//this is not for development, but for PS.
+//this line is super critical for development.
+
+using namespace std;
+
+ll n;
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    cin>>n;
+    ll result = 1;
+    ll cnt2, cnt5;
+    cnt2 = cnt5 = 0;
+
+    for (ll i =1; i<=n; i++) {
+        ll tmp = i;
+        while (tmp % 2 == 0) {
+            cnt2++; tmp /= 2;
+        }
+        while (tmp % 5 == 0) {
+            cnt5++; tmp /= 5;
+        }
+
+        result = (result % MOD) * (tmp % MOD);
+        result %= MOD;
+    }
+
+    ll diff = cnt2 - cnt5;
+    if (diff < 0) {
+        cnt5 -= cnt2;
+        while (cnt5--) {
+            result = (result % MOD) * 5;
+            result %= MOD;
+        }
+    }
+    else {
+        cnt2 -= cnt5;
+        while (cnt2--) {
+            result = (result % MOD) * 2;
+            result %= MOD;
+        }
+    }
+
+    string res_s = to_string(result);
+    ll str_diff = 5 - res_s.size();
+    while (str_diff--) { cout << '0'; }
+    cout << result;
+}
+
+
+int main(){
+    fastIO();
+    result();
+    return 0;
+}
+
diff --git "a/\354\235\264\354\235\200\354\264\235/week5/backjoon_1629.cpp" "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1629.cpp"
new file mode 100644
index 0000000..dc234e1
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1629.cpp"
@@ -0,0 +1,67 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 100010
+#define MOD 1'000'000'007
+using namespace std;
+
+
+ll modpow(ll base, ll exp) {
+    ll res = 1;
+    while (exp) {
+        if (exp & 1) res = res * base % MOD;
+        base = base * base % MOD;
+        exp >>= 1;
+    }
+    return res;
+}
+
+ll modinv(ll x) {
+    return modpow(x, MOD - 2);
+}
+
+ll ncr(ll N, ll K) {
+    if (K < 0 || K > N) return 0;
+    if (K == 0 || K == N) return 1;
+    K = min(K, N - K);
+    ll res = 1;
+    for (ll i = 1; i <= K; ++i) {
+        res = res * (N - i + 1) % MOD;
+        res = res * modinv(i) % MOD;
+    }
+    return res;
+}
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    ll n;
+    cin >> n;
+    ll rec_count = 2LL * ncr(2 * n - 1, n - 1) % MOD;
+    ll dp_count = n * n % MOD;
+
+    cout << rec_count << " " << dp_count << "\n";
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week5/backjoon_1699.cpp" "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1699.cpp"
new file mode 100644
index 0000000..dd47938
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_1699.cpp"
@@ -0,0 +1,56 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MOD 100000
+#define MAX 100010
+//this is not for development, but for PS.
+//this line is super critical for development.
+
+using namespace std;
+
+ll n;
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    cin>>n;
+    vector<ll> dp;
+    dp.resize(n+1);
+
+    for (int i=0; i<=n; i++) {
+        dp[i] = i;
+    }
+
+    for (ll i=1; i<=n; i++) {
+        dp[i] = i;
+        for (ll j=1; j*j <= i; j++) {
+            dp[i] = min(dp[i], dp[i - j*j]+1);
+        }
+    }
+
+    cout << dp[n];
+}
+
+
+int main(){
+    fastIO();
+    result();
+    return 0;
+}
+
diff --git "a/\354\235\264\354\235\200\354\264\235/week5/backjoon_24419.cpp" "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_24419.cpp"
new file mode 100644
index 0000000..dc234e1
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week5/backjoon_24419.cpp"
@@ -0,0 +1,67 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 100010
+#define MOD 1'000'000'007
+using namespace std;
+
+
+ll modpow(ll base, ll exp) {
+    ll res = 1;
+    while (exp) {
+        if (exp & 1) res = res * base % MOD;
+        base = base * base % MOD;
+        exp >>= 1;
+    }
+    return res;
+}
+
+ll modinv(ll x) {
+    return modpow(x, MOD - 2);
+}
+
+ll ncr(ll N, ll K) {
+    if (K < 0 || K > N) return 0;
+    if (K == 0 || K == N) return 1;
+    K = min(K, N - K);
+    ll res = 1;
+    for (ll i = 1; i <= K; ++i) {
+        res = res * (N - i + 1) % MOD;
+        res = res * modinv(i) % MOD;
+    }
+    return res;
+}
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    ll n;
+    cin >> n;
+    ll rec_count = 2LL * ncr(2 * n - 1, n - 1) % MOD;
+    ll dp_count = n * n % MOD;
+
+    cout << rec_count << " " << dp_count << "\n";
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week6/backjoon_11051.cpp" "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_11051.cpp"
new file mode 100644
index 0000000..3a59bc1
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_11051.cpp"
@@ -0,0 +1,64 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 100010
+#define MOD 10'007
+using namespace std;
+
+
+ll modpow(ll base, ll exp) {
+    ll res = 1;
+    while (exp) {
+        if (exp & 1) res = res * base % MOD;
+        base = base * base % MOD;
+        exp >>= 1;
+    }
+    return res;
+}
+
+ll modinv(ll x) {
+    return modpow(x, MOD - 2);
+}
+
+ll ncr(ll N, ll K) {
+    if (K < 0 || K > N) return 0;
+    if (K == 0 || K == N) return 1;
+    K = min(K, N - K);
+    ll res = 1;
+    for (ll i = 1; i <= K; ++i) {
+        res = res * (N - i + 1) % MOD;
+        res = res * modinv(i) % MOD;
+    }
+    return res;
+}
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    ll n, k;
+    cin>>n>>k;
+    cout << ncr(n, k) << "\n";
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week6/backjoon_11401.cpp" "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_11401.cpp"
new file mode 100644
index 0000000..3a59bc1
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_11401.cpp"
@@ -0,0 +1,64 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 100010
+#define MOD 10'007
+using namespace std;
+
+
+ll modpow(ll base, ll exp) {
+    ll res = 1;
+    while (exp) {
+        if (exp & 1) res = res * base % MOD;
+        base = base * base % MOD;
+        exp >>= 1;
+    }
+    return res;
+}
+
+ll modinv(ll x) {
+    return modpow(x, MOD - 2);
+}
+
+ll ncr(ll N, ll K) {
+    if (K < 0 || K > N) return 0;
+    if (K == 0 || K == N) return 1;
+    K = min(K, N - K);
+    ll res = 1;
+    for (ll i = 1; i <= K; ++i) {
+        res = res * (N - i + 1) % MOD;
+        res = res * modinv(i) % MOD;
+    }
+    return res;
+}
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    ll n, k;
+    cin>>n>>k;
+    cout << ncr(n, k) << "\n";
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week6/backjoon_1654.cpp" "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_1654.cpp"
new file mode 100644
index 0000000..658d07e
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_1654.cpp"
@@ -0,0 +1,72 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 1000000
+#define MOD 1'000'000'007
+using namespace std;
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+ll k, n;
+vector<ll> v;
+
+
+int isPassed(int mid, const vector<ll> & data) {
+    ll p_ret = 0;
+    for (int i=0; i<k; i++) {
+        p_ret += data[i] / mid;
+    }
+    return p_ret >= n;
+}
+
+
+int binarySearch(ll high, const vector<ll>& data) {
+    ll low = 1;
+    ll mid;
+    ll res = 0;
+    while (low <= high) {
+        mid = (low + high) / 2;
+        if (isPassed(mid, data)) {
+            low = mid + 1;
+            if (res < mid) { res = mid; }
+        }
+        else { high = mid - 1; }
+    }
+    return res;
+}
+
+
+void result() {
+    cin>>k>>n;
+    v.resize(k);
+    ll currMax = 0;
+    for (int i=0; i<k; i++) {
+        cin >> v[i];
+        currMax = max(currMax, v[i]);
+    }
+
+    cout << binarySearch(currMax, v);
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week6/backjoon_1850.cpp" "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_1850.cpp"
new file mode 100644
index 0000000..22998a8
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_1850.cpp"
@@ -0,0 +1,43 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 100010
+#define MOD 1'000'000'007
+using namespace std;
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+void result() {
+    ll a, b;
+    cin>>a>>b;
+
+    ll currGcd = __gcd(a, b);
+
+    while (currGcd--) {
+        cout << 1;
+    }
+    cout << "\n";
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file
diff --git "a/\354\235\264\354\235\200\354\264\235/week6/backjoon_2805.cpp" "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_2805.cpp"
new file mode 100644
index 0000000..972ae34
--- /dev/null
+++ "b/\354\235\264\354\235\200\354\264\235/week6/backjoon_2805.cpp"
@@ -0,0 +1,72 @@
+#include <iostream>
+#include <algorithm>
+#include <vector>
+#include <stack>
+#include <queue>
+#include <set>
+#include <unordered_set>
+#include <unordered_map>
+#include <tuple>
+#include <map>
+#include <string>
+#include <cmath>
+#define ll long long
+#define weight first
+#define val second
+#define INF 987654321987654321
+#define MAX 1000000
+#define MOD 1'000'000'007
+using namespace std;
+
+void fastIO() {
+    std::ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+    cout.tie(nullptr);
+}
+
+ll k, n;
+vector<ll> v;
+
+
+int isPassed(int mid, const vector<ll> & data) {
+    ll p_ret = 0;
+    for (int i=0; i<k; i++) {
+        p_ret += max( data[i] - mid, 0ll);
+    }
+    return p_ret >= n;
+}
+
+
+int binarySearch(ll high, const vector<ll>& data) {
+    ll low = 1;
+    ll mid;
+    ll res = 0;
+    while (low <= high) {
+        mid = (low + high) / 2;
+        if (isPassed(mid, data)) {
+            if (res < mid) {res = mid;}
+            low = mid + 1;
+        }
+        else { high = mid - 1; }
+    }
+    return res;
+}
+
+
+void result() {
+    cin>>k>>n;
+    v.resize(k);
+    ll currMax = 0;
+    for (int i=0; i<k; i++) {
+        cin >> v[i];
+        currMax = max(currMax, v[i]);
+    }
+
+    cout << binarySearch(currMax, v);
+}
+
+int main() {
+    fastIO();
+    result();
+    return 0;
+}
\ No newline at end of file