#!/usr/bin/perl

use strict;
use warnings;

my $year = $ARGV[0] || 0;
print is_leap_year($year) ? "$year is a leap year.\n" : "$year isn't a leap year.\n";
exit;

sub is_leap_year {
   my $year = shift;
   return ($year % 400 == 0 || $year % 100 != 0 && $year % 4 == 0) ? 1 : 0;
}