#!/usr/bin/perl
use warnings;
use strict;

sub cookies {
    my $number = shift;
    return ('COOKIES ' x ($number - 1) . 'COOKIES' . 'S' x $number)
}

my $number  = 1;
my $cookies = "";

while ($cookies ne cookies($number)) {
    $number++;
    print 'Cookie monster: I want ', cookies($number), "!\n";
    chomp($cookies = <STDIN>);
}

print "Mmmm. $number COOKIES. :-)\n";