#include <bits/stdc++.h>
using namespace std;
const int a[] = {0, 1, 3, 6, 10, 15, 21, 28, 36, 45};
int main() {
  ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
  int n, m;
  string s;
  cin >> n >> s;
  for (int m = lower_bound(a, a + 10, n) - a, i = 0; i < m; i++)
    cout << s[a[i]];
}
