#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string a;
  cin >> a;
  string answer;
  int count = 1;
  for (int z = 0; z < n;) {
    answer += a[z];
    z = z + count;
    count++;
  }
  cout << answer << endl;
}
