#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string a;
  char b[n];
  cin >> a;
  int i, j = 1;
  for (i = 0; i < n; i = i + j) {
    b[j - 1] = a[i];
    j++;
  }
  for (i = 0; i < j - 1; i++) cout << b[i];
  return 0;
}
