#include <bits/stdc++.h>
const int maxn = 60;
#pragma warning(disable : 4996)
char a[maxn];
using namespace std;
int main() {
  int len = 0;
  while (~scanf("%d", &len)) {
    for (int i = 1; i <= len; i++) {
      scanf(" %c", &a[i]);
    }
    for (int i = 1; (i * (i + 1) / 2) <= len; i++) {
      cout << a[i * (i + 1) / 2];
    }
    cout << endl;
  }
  return 0;
}
