#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  vector<int> v;
  v.push_back(0);
  for (int i = 1; i < 99; ++i) v.push_back(v.back() + i);
  for (int vi : v)
    if (vi < n) cout << s[vi];
  return 0;
}
