#include <bits/stdc++.h>
using namespace std;
char a[200010], c[200010];
int main() {
  int n, m, t, i, j, k, f = 1;
  cin >> t;
  cin >> a;
  for (i = 0; i < t;) {
    cout << a[i];
    i = f + i;
    f++;
  }
  cout << endl;
  return 0;
}
