b0, c0 = map(int, input().split())
b1, c1 = map(int, input().split())
c0 %= b0
c1 %= b1
for i in range(b0 * b1 + 1):
    if i % b0 == c0 and i % b1 == c1:
        print(i)
        exit()
print("NaN")