#!/usr/bin/perl

use strict;

print "ackermann($ARGV[0], $ARGV[1])\n";

print ackermann($ARGV[0], $ARGV[1]);

sub ackermann
{
    my ($x, $y) = @_;

    my @stack = ();
    while((defined $x and $x > 0) ||
          ((scalar @stack) != 0))
    {
        if($x == 0) { $x = pop @stack, $y++; }
        elsif($y == 0) { $y = 1, $x--; }
        else { $y--, push @stack, ($x-1); }
    }

    return ($y + 1);
}