(define (poky L K)
  (let* ((n (quotient L 2)))
    (cond [(= L 1) 0]
          [(odd? L) (* (quotient n K) K)]
          [(= (remainder n K) 0) (* (- (quotient n K) 1) K)]
          [else (* (quotient n K) K)])))

(define (main args)
  (let* ((L (read))
         (K (read)))
    (print (poky L K))) 0)