#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[]) {
  string encriptada;
  int n, k;
  k = 0;
  cin >> n;
  cin >> encriptada;
  for (int i = 1; k != n; i++) {
    k += i;
    cout << encriptada[k - 1];
  }
  return 0;
}
