my $num1 = shift;
my $flag = shift;

##</code><code>##

my ($num1, $flag) = @_;

##</code><code>##

use strict;
use warnings;

sub fact {
   my ($n) = @_;
   return 1 if $n == 0;
   return $n * fact($n-1);
}

die "usage\n" if !@ARGV;

print(fact($ARGV[0]), "\n");