use strict;
use warnings;

sub is_valid_isbn {
	my @digits = split //, shift;

	(@digits == 13) or return;

	my $n = 0;
	foreach(0..12){
		$n += $digits[$_] * ($_ % 2 ? 3 : 1);
	}

	return ($n % 10 == 0);
}

foreach(qw( 9784062772211 9784150315684 )){
	printf("%s => %s\n", $_, (is_valid_isbn($_) ? "OK" : "NG"));
}