#include <bits/stdc++.h>
int main() {
  int length, skip = 1;
  scanf("%d", &length);
  char string[length];
  scanf("%s", string);
  for (int i = 0; i < length; i++) {
    int cons = skip;
    while (--cons) {
      i++;
    }
    printf("%c", string[i]);
    skip++;
  }
  printf("\n");
  return 0;
}
