(define next (read))
(define (peek) next)
(define (get) (define t next) (set! next (read)) t)

(define (parse-atom) (get))

(define (parse-mul)
  (define cur (parse-atom))
  (define c (peek))
  (define (recur)
  (when (or (eq? c '*) (eq? c '/)) (begin
      (get)
      (define m2 (parse-atom))
      (set! cur (if (eq? c '*) (* cur m2) (/ cur m2)))
      (set! c (peek))
      (recur))
  ))
  (recur)
  cur
)

(define (parse-add)
  (define cur (parse-mul))
  (define c (peek))
  (define (recur)
  (when (or (eq? c '+) (eq? c '-)) (begin
      (get)
      (define m2 (parse-mul))
      (set! cur (if (eq? c '+) (+ cur m2) (- cur m2)))
      (set! c (peek))
      (recur))
  ))
  (recur)
  cur
)
(display (parse-add))