McCarthy's 91 Function - Non Recursive

#!/usr/bin/perl -w

use strict;
use warnings;

my $n = <STDIN>;
chomp($n);

mprint($n, 1);

sub mprint {
    my $n = shift;
    my $level = shift;

    while($level > 0) {
        print tostring($n, $level)."\n";
        if($n <= 100) { $n += 11; $level++; }
        else { $n -= 10; $level--; }
    }

    print tostring($n, $level)."\n";
}

sub tostring {
    my $n = shift;
    my $level = shift;

    return "$n" if $level <= 0;
    return "M($n)" if $level == 1;
    return "M(".tostring($n, $level-1).")";
}