(module hash mzscheme
  (define (main argv)
    (let* ([n (string->number (vector-ref argv 0))]
	   [hash (make-hash-table 'equal)]
	   [accum 0]
	   [false (lambda () #f)])
      (let loop ([i 1])
	(unless (> i n)
	  (hash-table-put! hash (number->string i 16) i)
	  (loop (add1 i))))
      (let loop ([i n])
	(unless (zero? i)
	  (when (hash-table-get hash (number->string i) false)
	    (set! accum (+ accum 1)))
	  (loop (sub1 i))))
      (printf "~s~n" accum)))

  (main (current-command-line-arguments)))