#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, x, counter = 0;
  int add = 1;
  bool first = true;
  cin >> n;
  string entry, edited = "";
  cin >> entry;
  while (entry[counter] != NULL) {
    edited += entry[counter];
    counter += add;
    add++;
  }
  cout << edited;
}
