/* Non-recursive, debatably readable solution to
   <https://twitter.com/TimSweeneyEpic/status/1265451572353552384>
 */

#include <stdio.h>
#include <stdlib.h>

void PrintXY(int n) {
  char s[n+1];
  int i;
  for (i = 0; i < n; i++) s[i] = 'X';
  s[n] = '\0';

  while (i >= 0) {
    puts(s);

    for (i = n-1; i >= 0; i--) {
      if ('X' != s[i]) continue;
      s[i] = 'Y';
      for (int j = i+1; j < n; j++) s[j] = 'X';
      break;
    }
  }
}

int main(int argc, char **argv) {
  PrintXY(atoi(argv[1]));
  return 0;
}