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

my @evens;
my $n = 0;
my $number_to_give_up_at = 21;

# $#evens will contain value of index of last element in @evens array
while ($n++ < $number_to_give_up_at and $#evens < 9){
push @evens, $n if $n % 2 == 0;
}

print join("\n", @evens);