; for で一文字ずつ比較する
(defun main ()
  (let* ((_ (read))
         (s1 (read-line))
         (s2 (read-line))
         (ans (loop for c1 across s1
                    for c2 across s2
                    count (char/= c1 c2))))
    (declare (ignore _))
    (princ ans)
    (terpri)))
(main)