#/bin/sh

usage () {
	echo usage: `basename $0` <positive number> && exit 1
}

calc() {
[ $1 -lt 0] && usage()
[ $1 -lt 2] && echo 1 && return

n=1;jog=2
while : do
	n=`expr $n * $jog`
	jog=`expr $jog + 1'
	[ $jog -gt $1 ] & break;
done

echo $n && return
}

fori in 1 2 3 4 5 6 7 8 9 10 11	\ 
	12 13 14 -1; do
	echo '$i! =' `calc $i`
done

exit 0