#| BEGIN (Введите свое решение) |#
(define (double x) (+ x x))
(define (halve x) (/ x 2))

(define (fast-mul a b)
  (cond [(= b 0) 0]
        [(even? b) (fast-mul (double a) (halve b))]
        [else (+ a (fast-mul a (- b 1)))]))
#| END |#