(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((n (read))
         (a (make-array n :element-type 'integer))
         (res 0))
    (dotimes (i n) (setf (aref a i) (read)))
    (loop for i below (1- n) do
          (loop for j from (1+ i) below n do
                (setf res (max res (logxor (aref a i) (aref a j))))))
    (format t "~d~%" res)))

(main)