#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, i;
  cin >> n;
  char str[n];
  cin >> str;
  int k = 1;
  char arr[n], l = 0;
  for (i = 0; i < n; i = i + k) {
    arr[l] = str[i];
    k++;
    l++;
  }
  for (i = 0; i < l; i++) cout << arr[i];
}
