diff --git a/__main__.py b/__main__.py
index 53c2c43..c1a74e5 100644
--- a/__main__.py
+++ b/__main__.py
@@ -1,5 +1,13 @@
-def main() -> None:
-    print("Hello world")
-
-
-main()
+from doomsday.date import is_valid_date
+from doomsday.algorithm import get_weekday_for_date
+
+def input_date() -> None:
+    """Asks for a date and check if its valid"""
+    time_str = str(input("Enter date in this format yyyy-mm-dd \n >>"))
+    if is_valid_date(time_str):
+        result = get_weekday_for_date(time_str)
+        print(f"The day of the week is: {result}")
+    else:
+        return False
+
+input_date()
\ No newline at end of file
diff --git a/doomsday/algorithm.py b/doomsday/algorithm.py
index cf81d60..15ceb88 100644
--- a/doomsday/algorithm.py
+++ b/doomsday/algorithm.py
@@ -1,2 +1,46 @@
-def get_weekday_for_date(date: str) -> str:
-    return "Sunday"
+def get_anchor_day(year: int) -> int:
+
+    # Extract the century
+    century = year // 100 * 100
+
+    # Century offset
+    anchor = ((century // 100) % 4) * 5
+
+    # Add the offset based on the century
+    anchor = (anchor + 2) % 7
+
+    return anchor
+
+
+def get_doomsday(year):
+
+    # Extract the last two digits of the year
+    year_digits = year % 100
+
+    # Divide by 12 and take the remainder
+    quotient = year_digits // 12
+    remainder = year_digits - 12*quotient
+
+    # Apply the doomsday formula
+    doomsday = (remainder // 4)
+
+    doomsday = (quotient+remainder+doomsday+get_anchor_day(year)) % 7
+    
+    return doomsday
+
+def get_weekday_for_date(date: str):
+
+    year, month, day = map(int, date.split("-"))
+
+    anchor_day = get_anchor_day(year)
+
+    # Get Doomsday
+    doomsday = get_doomsday(year)
+
+    # Calculate day_of_week_index
+    day_of_week_index = (day - doomsday + anchor_day) % 7
+
+    days_of_week = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
+
+    # Get the corresponding day in the array
+    return days_of_week[day_of_week_index]
diff --git a/doomsday/date.py b/doomsday/date.py
index 0f8e737..bb66af8 100644
--- a/doomsday/date.py
+++ b/doomsday/date.py
@@ -1,2 +1,30 @@
-def is_valid_date(date: str) -> bool:
-    return True
+def is_valid_date(date: str):
+    try:
+        if not date:
+            raise ValueError("Empty date string")
+
+        date = date.split("-", 3)
+        if len(date) != 3:
+            raise ValueError("Invalid date format")
+
+        year = int(date[0]) if date[0] and int(date[0]) >= 1583 else None
+        month = int(date[1]) if date[1] and 1 <= int(date[1]) <= 12 else None
+        if year is None:
+            raise ValueError("Invalid year")
+        if month is None:
+            raise ValueError("Invalid month")
+        if date[2] and month in [1, 3, 5, 7, 8, 10, 12]:
+            day = int(date[2]) if 1 <= int(date[2]) <= 31 else None
+        elif date[2] and month in [4, 6, 9, 11]:
+            day = int(date[2]) if 1 <= int(date[2]) <= 30 else None
+        elif date[2] and month == 2:
+            day = int(date[2]) if is_leap_year(year) and int(date[2]) > 0 and int(date[2]) < 30 or not is_leap_year(year) and int(date[2]) > 0 and int(date[2]) < 29 else None
+        if day is None:
+            raise ValueError("Invalid day")
+        return True
+
+    except ValueError as e:
+        print(e)
+
+def is_leap_year(year: int) -> bool:
+    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)