#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s, ss = "";
  cin >> n >> s;
  int i = 0, j = 1;
  while (i < n) {
    ss += s[i];
    i += j;
    j += 1;
  }
  cout << ss << endl;
}
