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
    if b0 * b1 == i:
        print("NaN")