#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a = 0;
  string s1, s2;
  cin >> n >> s1;
  for (int i = 0; i < n; i += a) {
    cout << s1[i];
    ++a;
  }
  cout << endl;
  return 0;
}
