#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string N;
  string ANS = "";
  cin >> N;
  int m = 2;
  int s = 0;
  for (int i = 0; i < N.size(); i += s) {
    ANS += N[i];
    if (i == 0) {
      s += 2;
    } else {
      ++s;
    }
  }
  cout << ANS << endl;
  return 0;
}
