#include <bits/stdc++.h>
using namespace std;
int main() {
  int i, k, n;
  string fs, s;
  cin >> n >> s;
  k = 0;
  fs = s[0];
  for (i = 1; k + i < n; i++) {
    k = k + i;
    fs = fs + s[k];
  }
  cout << fs;
}
