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