#include <bits/stdc++.h>
int main() {
  int t = 0, i, n;
  char str[60];
  scanf("%d", &n);
  scanf("%s", &str);
  for (i = 1; t < n; i = i + 1) {
    printf("%c", str[t]);
    t += i;
  }
  return 0;
}
