if [ $# -eq 1 ]; then

	A=$1

	if [[ $A =~ ^[\-0-9]+$ ]] && ((A >= 0)); then

		if [ $A -gt 20 ]; then
			echo "Entered number exceeds maximum, aborting..."
			exit 1;
		fi

		echo "Valid input, calculating faculty..."
		si="0"
		i="1"
		ii=$((A+1))
		r="1"
		while [ $i -lt $ii ] && [ $si -lt 30 ]; do
			si=$((si+1))
			r=$((i*r))
			i=$((i+1))
		done
		echo "Faculty of $A is $r"

	else
		echo "Parameter is not a valid number!"
		exit 1;
	fi
else
	echo "Aufrufen: faculty.bash number";
	exit 1;
fi;