(defun help-func (n list)
	(cond
		((= n 1) (car list))
		(T (help-func (1- n) (cdr list)))))
 
(defun no-nth (n list)
	(cond
 		((or (< n 0) (>= n (length list))) 'invalid-index)
		(T (help-func n list))))
 
(print (no-nth 2 '(1 6 7)))
(print (no-nth 21 '(1 2 3)))