mod = 998244353


def mul(l, r):
    la, lb, lc, ld = l
    ra, rb, rc, rd = r
    return (la*ra+lb*rc) % mod, (la*rb+lb*rd) % mod, (lc*ra+ld*rc) % mod, (lc*rb+ld*rd) % mod


def inv(x):
    a, b, c, d = x
    det = (a * d - b * c) % mod
    det_inv = pow(det, mod-2, mod)
    y = d, -b, -c, a
    return tuple(i * det_inv % mod for i in y)


def mat_pow(a, x):
    b = 1, 0, 0, 1
    while x:
        if x % 2 == 1:
            b = mul(b, a)
        a = mul(a, a)
        x //= 2
    return b


def bsgs(mat, a, b):
    k = 10 ** 5 + 100

    mat_k = mat_pow(mat, k)
    giant = {}
    x = a
    for i in range(k):
        giant[x] = i
        x = mul(mat_k, x)

    mat_inv = inv(mat)
    x = b
    for i in range(k):
        if x in giant:
            return giant[x] * k + i

        x = mul(mat_inv, x)

    return None


a, b, p, q = map(int, input().split())

mat = a, -b, 1, 0

start = a ** 2 - 2 * b, 0, a, 0
finish = p, 0, q, 0
n = bsgs(mat, start, finish) + 2
print(n)