#lang scheme/base
(require scheme/cmdline)

(define (generate receive-ch n)
  (if (zero? n)
      receive-ch
      (let ([ch (make-channel)])
        (thread (lambda ()
                  (let loop ()
                    (channel-put ch (add1 (channel-get receive-ch)))
                    (loop))))
        (generate ch (sub1 n)))))

(let ([n (command-line #:args (n) (string->number n))])
  (let* ([start-ch (make-channel)]
         [end-ch (generate start-ch 500)])
    (let loop ([n n][total 0])
      (if (zero? n)
          (printf "~a\n" total)
          (begin
            (channel-put start-ch 0)
            (loop (sub1 n)
                  (+ total (channel-get end-ch))))))))