(defvar L)
(defvar K)
(defvar temp)
(setq temp (read-from-string (concatenate 'string "(" (read-line) ")" )))
(setq L (nth 0 temp ))
(setq K (nth 1 temp ))
(defvar ans)
(setq ans (floor L (* K 2)))
(if (eq (* ans K 2) L) (setq ans (decf ans)))
(format 't "~d~%" (* ans K))