import math
def Chinese_Surplus_Theorem(b1,b2,m1,m2):
    def Euclidean_Algorithm(a,b,d):
        a,b = max(a,b),min(a,b)
        if a == d and b == 0:
            return 1,0
        div,mod = divmod(a,b)
        nx,ny = Euclidean_Algorithm(b,mod,d)
        res = (ny,nx - div*ny)
        return res
    d = math.gcd(m1,m2)
    if m1 < m2:
        m1,m2 = m2,m1
        b1,b2 = b2,b1
    if b1 % d != b2 % d:return 0,0
    p,q = Euclidean_Algorithm(m1,m2,d)
    s = (b2-b1)//d
    return (b1 + s*m1*p) % (m1*m2//d) ,m1*m2//d

b0,c0 = map(int,input().split())
b1,c1 = map(int,input().split())
c0 %= b0
c1 %= b1
x,y = Chinese_Surplus_Theorem(c0,c1,b0,b1)
if c0 == c1 == 0:
    print(0)
elif x == 0:
    print("NaN")
else:
    print(x)