#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t, f, h = 0, z = 0, x = 0;
  char a[100];
  cin >> t;
  for (int i = 0; i < t; i++) {
    cin >> a[i];
  }
  while (t > 0) {
    z++;
    t = t - z;
  }
  for (int y = 0; y < z; y++) {
    h = h + y;
    cout << a[h];
  }
  return 0;
}
