(defun main (&rest argv)
  (declare (ignorable argv))
  (let* ((x (read))
         (y (read))
         (z (read)))
    (format t "~d~%" (+ (min (abs (- x y)) z)
                        (min x y)
                        (floor (- z (min z (abs (- x y)))) 2)))))

(main)