#include <bits/stdc++.h>
using namespace std;
int main() {
  string s, ans;
  int n;
  cin >> n;
  cin >> s;
  int idx = 1, cnt = 2;
  while (idx - 1 < n) {
    ans += s[idx - 1];
    idx += cnt;
    cnt++;
  }
  cout << ans;
}
