#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string t;
  cin >> t;
  char b;
  int i = 0;
  int sum = 0;
  while (i < n) {
    b = t[i];
    sum += 1;
    i += sum;
    cout << b;
  }
  cout << endl;
}
