#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n, i = 0, j = 1;
  cin >> n;
  char c[n];
  cin >> c;
  while (i <= n) {
    cout << c[i];
    i = i + j + 1;
    j++;
  }
  return 0;
}
