#include <bits/stdc++.h>
using namespace std;
int main() {
  int test;
  cin >> test;
  string s, r;
  cin >> s;
  int j = 0;
  for (int i = 0; i < test; i += j) {
    r.push_back(s[i]);
    j++;
  }
  cout << r;
  return 0;
}
