#include <stdio.h>

#define FILL 'X'


int main()
{
  int i, r = 0;
  char s[39 + 1];

  s[r++] = FILL; s[r] = '\0';

  for(i = 1; i <= 20; i++)
  {
    printf("%39s\n", s);
    if(r > 40) // КОСТЫЛЬ
    	exit();
    s[r++] = FILL; s[r++] = FILL; s[r] = '\0';
  }
}