chore: add fyi program

fyi/main.cpp

@@ -0,0 +1,16 @@
+#include <iostream>
+#include <string>
+using namespace std;
+
+int main(){
+    string number = "";
+    cin >> number;
+    if (number.substr(0,3) == "555"){
+        cout << "1" << endl;
+    }
+    else{
+        cout << "0" << endl;
+    }
+    
+    return 0;
+}