int main()
{
  char is_open[100] = { 0 };
  int pass, door;

  
  for (pass = 0; pass < 100; ++pass)
    for (door = pass; door < 100; door += pass+1)
      is_open[door] = !is_open[door];

  
  for (door = 0; door < 100; ++door)
    printf(, door+1, (is_open[door]?  : ));

  return 0;
}