sub hanoi 
{
   my ($n, $start, $end, $extra) = @_;
   if ($n == 1) 
   {
      print "Move disk #1 from $start to $end.\n";
   } 
   else 
   {
      hanoi($n-1, $start, $extra, $end);
      print "Move disk #$n from $start to $end.\n";
      hanoi($n-1, $extra, $end, $start);
   }
}