diff --git a/4C Registration System/4C.cpp b/4C Registration System/4C.cpp
new file mode 100644
index 0000000..a9bf2c0
--- /dev/null
+++ b/4C Registration System/4C.cpp	
@@ -0,0 +1,39 @@
+#include<bits/stdc++.h>
+using namespace std;
+using ll = long long;
+
+void solve()
+{
+    int n;
+    cin>>n;
+    unordered_map<string,int>m;
+    for(int i=0; i<n; ++i)
+    {
+        string s;
+        cin>>s;
+        auto it= m.find(s);
+        if(it==m.end())
+        {
+            m[s];
+            cout<<"OK"<<endl;
+        }
+        else
+        {
+            m[s]++;
+            s=s+to_string(m[s]);
+            m[s];
+            cout<<s<<endl;
+        }
+    }
+}
+
+int main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    int TC = 1;
+    //cin >> TC;
+    //cin.ignore();
+    while (TC--) solve();
+}
\ No newline at end of file