#!/usr/bin/env gosh

(define (can-resolve? lst)
  (if (not (= 0 (list-ref lst 1)))
      #t
      (if (or (= 0 (list-ref lst 0))
              (= 0 (list-ref lst 2)))
          #f
          #t)))

(define (count d lst)
  (let ((d12 (- (cadr lst) (car lst)))
        (d23 (- (cadr lst) (caddr lst))))
    (if (positive? (* d12 d23))
        0
        (+ 1
           (div (min (abs d12) (abs d23)) d)))))

(let* ((d (read))
      (h1 (read))
      (h2 (read))
      (h3 (read))
      (hlist `(,h1 ,h2 ,h3)))
  (if (or (not (can-resolve? hlist))
          (= d 0))
      (display -1)
      (display (count d hlist)))
  (newline))