d = int(input())
h = [0] * 3
h[0] = int(input())
h[1] = int(input())
h[2] = int(input())

if h[0] > h[1] and h[2] > h[1]:
    ans = 0
elif h[0] < h[1] and h[2] < h[1]:
    ans = 0
elif min(h) == 0:
    ans = -1
elif min(h) == max(h):
    ans = 1
else:
    if h[2] >= h[0]:
        tmp = h[0]
        h[0] = h[2]
        h[2] = tmp

    if (h[0] - h[1]) > (h[1] - h[2]):
        ans = (h[1]-h[2]) // d
        if (h[1]-h[2]) % d == 0:
            ans += 1
    else:
        ans = (h[0]-h[1]) // d
        if (h[0]-h[1]) % d == 0:
            ans += 1

print(ans)