#!/usr/local/bin/perl
# Jaime Prilusky, 2003

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

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