#include <bits/stdc++.h>
using namespace std;
set<int> used;
int main() {
  int x;
  string s, so;
  cin >> x >> s;
  int i = 0;
  int j = 1;
  while (i < x) {
    so += s[i];
    i += j;
    j++;
  }
  cout << so;
}
