#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[]) {
  int N;
  cin >> N;
  string s;
  cin >> s;
  int i = 0;
  int skip = 1;
  while (i < N) {
    cout << s[i];
    i += skip;
    skip++;
  }
  cout << endl;
  return 0;
}
