(defun count-down ()
  (format t "~%Please type a number...")
  (let ((answer (read)))
    (if (not (numberp answer)) (count-down) 
      (cond ((< answer 0) (do ((current-number answer (+ current-number 1)))
			    ((= current-number 0) nil)
			  (print current-number)))
	  ((> answer 0) (do ((current-number answer (- current-number 1)))
			    ((= current-number 0) nil)
			  (print current-number)))
	  (t (print answer))))))