#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t, n, m;
  string a;
  cin >> n >> a;
  string r = "";
  for (int i = 0; i < n;) {
    r += a[i];
    int k = r.size();
    i = (k * (k + 1)) / 2;
  }
  cout << r;
  return 0;
}
