#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k = 0, i = 0;
  cin >> n;
  string s, s1 = "";
  cin >> s;
  while (i < n) {
    s1 += s[i];
    k++;
    i += k;
  }
  cout << s1;
}
