#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i;
  cin >> n;
  string s;
  cin >> s;
  int k = 0;
  ;
  int sum = 0, summ = 0;
  while (sum != n) {
    k = k + 1;
    sum = k * (k + 1) / 2;
  }
  for (i = 1; i <= k; i = i + 1) {
    summ = summ + i;
    cout << s[summ - 1];
  }
}
