#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, f = 1;
  ;
  string s, ans = "";
  scanf("%d", &n);
  cin >> s;
  for (int i = 0; i < n; i += f) {
    ans += s[i];
    f++;
  }
  cout << ans << endl;
}
