#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[]) {
  int n, i, c, g;
  g = 0;
  string s, ans;
  cin >> n >> s;
  for (i = 1; g < n; i++) {
    g = ((i * (i + 1)) / 2);
    ans.push_back(s[g - 1]);
  }
  cout << ans << "\n";
  return 0;
}
