def idsigma(veg, meat, c, max_eat):
    if meat < c:
        return 0
    else:
        eat_veg = 0
        eat_meat = 0
        count = 0
        eat = max_eat + 1
        while eat > max_eat:
            eat_veg = meat // c - count
            eat_meat = eat_veg * c
            eat = eat_veg + eat_meat
            count += 1
        return eat_veg


a, b, c, d = (int(x) for x in input().split())
idsigma(a, b, c, d)