print "Number to test: ";
$prime=<>;


        $t=($prime-1);

sub fac {
        my ($n) = @_;

        if ($n < 2) {
                return $n;
        }
        else {
                return $n *fac($n-1);
        }
}

$r = ((fac($t))+1);


if ($r % $prime) {
        print "not prime\n";
} else {
print "prime\n";
}