while(<>){
	chomp;

	$_ = 'Use YYYY-MM-DD format' unless s/^(\d{4})-(\d\d)-(\d\d)$/
	$1<1 || $2<1 || $3<1 ? 'Year, month, and day must be greater than 0' :
	$2>12 ? 'Month must be less than 13' :
	$3>31 ? 'Day must be less than 32' :
	$3==30&&$2==2 ? 'February has less than 30 days' :
	$3==29 && $2==2 && $1%4!=0 ? 'February only has 29 days in a leap year' :
	$3==31 && $2 =~ m!0[2469]|11! ? '30 days hath September, yada yada..' : $_ /e;

	print ": $_ :\n";
}