#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  string S, result;
  cin >> N >> S;
  int i = 0, j = 0;
  while (i < N) {
    result += S[i];
    j++;
    i = i + j;
  }
  cout << result << endl;
  return 0;
}
