#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  string st;
  cin >> st;
  long long z = 1;
  for (long long i = 0; i < n; i++) {
    cout << st[i];
    i = i + z;
    z++;
  }
  cout << "\n";
}
