(defun main (&rest args)
  (declare (ignorable args))
  (let* ((x (sort (loop repeat 4 collect (read)) #'<)))
    (loop for (x1 x2) on x
          while x2
          when (/= (1+ x1) x2)
            do (format t "No~%")
               (return-from main))
    (format t "Yes~%")))

(main)