#include <bits/stdc++.h>
using namespace std;
int main() {
  std::ios::sync_with_stdio(false);
  int chars;
  string str, output;
  cin >> chars >> str;
  for (int i = 0, n = 1; i < chars; i = i + n, n++) {
    output += str[i];
  }
  cout << output << endl;
  return 0;
}
