sub days_in_month 
{
    my ( $month, $year ) = @_;

    my @days_in_month = 
        qw/ 31 28 31 30 31 30
            31 31 30 31 30 31 /;

    if ( $month == 1 ) 
    {
        return 29 if is_leap_year( $year );
    }
    return $days_in_month[ $month ];
}

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