#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i = 0, j = 0;
  cin >> n;
  char ch[n];
  cin >> ch;
  while (ch[j] != '\0') {
    cout << ch[j];
    j += (i + 1);
    i++;
  }
  return 0;
}
