use strict;
use warnings;

my $num;
my $cal = 0;

print "Please enter the number. ";

$num = <STDIN>;
chomp $num;

Factorial ($num);
print "result : " . $cal . "\n";

sub Factorial {
	$num = shift;

	$cal += $num;
	$num--;
	if ($num > 0) {
		Factorial ($num);
	}
}