from math import gcd


def linear_congruence(a: int, b: int, m: int) -> tuple[int, int] | tuple[None, None]:
    # a x = b (mod m)
    g = gcd(a, m)
    if b % g != 0:
        return None, None

    a2 = a // g
    b2 = b // g
    m2 = m // g
    # a' x = b' (mod m')
    x = b2 * pow(a2, -1, m2) % m2
    return x, m2


def crt2(r1, m1, r2, m2):
    # x = r1 (mod m1)
    # x = r1 + m1 t
    # r1 + m1 t = r2 (mod m2)
    # m1 t = r2 - r1 (mod m2)

    t, m = linear_congruence(m1, r2 - r1, m2)
    if t is None:
        return None

    x = r1 + m1 * t
    return x


B0, C0 = map(int, input().split())
B1, C1 = map(int, input().split())

ans = crt2(C0 % B0, B0, C1 % B1, B1)
if ans is None:
    print('NaN')
else:
    print(ans)