diff --git a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.cpp b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.cpp
index 328ecdf..985c5a2 100644
--- a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.cpp	
+++ b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.cpp	
@@ -1,3 +1,10 @@
+#include <string>
+#include <unordered_map>
+#include <stdexcept>
+#include <iostream>
+
+using namespace std;
+
 class Solution {
 public:
     int romanToInt(string s) {
@@ -7,6 +14,9 @@ class Solution {
         int i = 0;
 
         while (i < n) {
+            if (i > 1 && d[s[i - 2]] < d[s[i - 1]] && d[s[i]] <= d[s[i - 1]]) {
+                throw invalid_argument("Invalid Roman numeric sequence " + s);
+            }
             if (i < n - 1 && d[s[i]] < d[s[i + 1]]) {
                 summ += d[s[i + 1]] - d[s[i]];
                 i += 2;
@@ -19,3 +29,10 @@ class Solution {
         return summ;
     }
 };
+
+int main() {
+    Solution sol;
+    // cout << sol.romanToInt("IIXX") << endl; // Throws invalid_argument
+    // cout << sol.romanToInt("MMD") << endl;  // Output: 2500
+    return 0;
+}
diff --git a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.java b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.java
index 6d7f9b1..f32c45c 100644
--- a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.java	
+++ b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.java	
@@ -17,6 +17,9 @@ public int romanToInt(String s) {
         int i = 0;
 
         while (i < n) {
+            if (i > 1 && d.get(s.charAt(i - 2)) < d.get(s.charAt(i - 1)) && d.get(s.charAt(i)) <= d.get(s.charAt(i - 1))) {
+                throw new IllegalArgumentException("Invalid Roman numeric sequence " + s);
+            }
             if (i < n - 1 && d.get(s.charAt(i)) < d.get(s.charAt(i + 1))) {
                 summ += d.get(s.charAt(i + 1)) - d.get(s.charAt(i));
                 i += 2;
@@ -28,4 +31,10 @@ public int romanToInt(String s) {
 
         return summ;
     }
+
+    public static void main(String[] args) {
+        Solution sol = new Solution();
+        // System.out.println(sol.romanToInt("IIXX")); // Throws IllegalArgumentException
+        // System.out.println(sol.romanToInt("MMD"));  // Output: 2500
+    }
 }
diff --git a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.js b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.js
index f1f97e2..564bb47 100644
--- a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.js	
+++ b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.js	
@@ -5,6 +5,9 @@ function romanToInt(s) {
     let i = 0;
 
     while (i < n) {
+        if (i > 1 && d[s[i - 2]] < d[s[i - 1]] && d[s[i]] <= d[s[i - 1]]) {
+            throw new Error(`Invalid Roman numeric sequence ${s}`);
+        }
         if (i < n - 1 && d[s[i]] < d[s[i + 1]]) {
             summ += d[s[i + 1]] - d[s[i]];
             i += 2;
@@ -16,3 +19,7 @@ function romanToInt(s) {
 
     return summ;
 }
+
+// Example Test Cases
+// console.log(romanToInt('IIXX')); // Throws Error
+// console.log(romanToInt('MMD'));  // Output: 2500
diff --git a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.py b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.py
index b4e0f48..dc63dd4 100644
--- a/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.py	
+++ b/Roman to Integer - Leetcode 13/Roman to Integer - Leetcode 13.py	
@@ -6,6 +6,9 @@ def romanToInt(self, s: str) -> int:
         i = 0
         
         while i < n:
+            if i > 1 and d[s[i - 2]] < d[s[i - 1]] and d[s[i]] <= d[s[i - 1]]:
+                raise ValueError(f"Invalid Roman numeric sequence {s}")
+
             if i < n - 1 and d[s[i]] < d[s[i+1]]:
                 summ += d[s[i+1]] - d[s[i]]
                 i += 2
@@ -16,3 +19,8 @@ def romanToInt(self, s: str) -> int:
         return summ
         # Time: O(n)
         # Space: O(1)
+
+# Example Test Cases
+# sol = Solution()
+# print(sol.romanToInt('IIXX')) # Raises ValueError
+# print(sol.romanToInt('MMD'))  # Output: 2500