func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     ios::sync_with_stdio(false), cin.tie(0);     int n;     string s;     cin >> n >> s;     if (count(s.begin(), s.end(), s[0]) == s.size() || s.size() == 1) {       cout <<  NO  << endl;     } else {       cout <<  YES  << endl;       for (int i = 0; i < s.size() - 1; i++) {         if (s[i] != s[i + 1]) {           cout << s[i] << s[i + 1];           exit(0);         }       }     }     return 0;   }   