#include <bits/stdc++.h>
using namespace std;
int main() {
  string s;
  vector<char> ar;
  char c;
  int j, t;
  cin >> j >> s;
  j = 1;
  for (int i = 1; i < s.size() + 1; i = (j * (j + 1)) / 2) {
    c = s[i - 1];
    ar.push_back(c);
    j++;
  }
  for (int i = 0; i < ar.size(); i++) {
    cout << ar[i];
  }
  ar.clear();
  return 0;
}
