# WRONG, DO NOT USE
use warnings; 
use strict; 
sub divmod { 
        my($a, $m) = @_; my($b, $x, $y, $n) = ($m, 1, 0);
        while (0 != $a) { $n = int($b / $a); ($a, $b, $x, $y) = ($b - $n * $a, $a, $y - $n * $x, $x); } 
        $y % $m; 
}