#include <bits/stdc++.h>
using namespace std;
int n;
string s;
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cin >> n >> s;
  for (int i = 0, j = 1; i < n; i += j, j++) cout << s[i];
  cout << '\n';
  return 0;
}
