func_code_string: #include <bits/stdc++.h>   using namespace std;   bool isprime(int n) {     for (int i = 2; i < n; i++) {       if (n % i == 0) {         return false;       }     }     return true;   }   int main() {     int n;     cin >> n;     string s;     cin >> s;     int diff = 1;     int i = 0;     while (i < n) {       cout << s[i];       i = i + diff;       diff++;     }   }   