#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, b = 0;
  char s[60];
  cin >> n;
  for (long long i = 1; i <= n; i++) cin >> s[i];
  for (long long i = 1; b + i <= n; i++) {
    cout << s[b + i];
    b += i;
  }
}
