B0, C0 = map(int, input().split())
B1, C1 = map(int, input().split())
for i in range(B0 * B1 + 1):
    if (i - C0) % B0 == 0 and (i - C1) % B1 == 0:
        print(i)
        break
else:
    print("NaN")