#include <bits/stdc++.h>   using namespace std;   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     int n;     cin >> n;     char s;     int d = 1, j = 1;     for (int i = 1; i <= n; i++) {       cin >> s;       j -= 1;       if (j == 0) {         cout << s;         d += 1;         j = d;       }     }     return 0;   }   