import sys



def inv_gcd(a, b):
    a %= b
    if a == 0: return b, 0
    s, t = b, a
    m0, m1 = 0, 1
    while t:
        u = s // t
        s -= t * u
        m0 -= m1 * u
        s, t = t, s
        m0, m1 = m1, m0
    if m0 < 0: m0 += b // s
    return s, m0

def crt(r, m):
    n = len(r)
    r0, m0 = 0, 1
    for i in range(n):
        r1, m1 = r[i] % m[i], m[i]
        if m0 < m1:
            r0, r1 = r1, r0
            m0, m1 = m1, m0
        if m0 % m1 == 0:
            if r0 % m1 != r1: return 0, 0
            continue
        g, im = inv_gcd(m0, m1)
        if (r1 - r0) % g: return 0, 0
        u1 = m1 // g
        x = (r1 - r0) // g % u1 * im % u1
        r0 += x * m0
        m0 *= u1
        if r0 < 0: r0 += m0
    return r0, m0



def main():
    a, b = map(int, input().split())
    c, d = map(int, input().split())
    r, m = [b, d], [a, c]
    z, mod = crt(r, m)
    if mod == 0:
        print('NaN')
    else:
        print(z)



if __name__ == '__main__':
    main()