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