def solve(B0, C0, B1, C1):
    C0 %= B0
    C1 %= B1
    for n in range(B0 * B1):
        if n % B0 == C0 and n % B1 == C1:
            return n
    return "NaN"


B0, C0 = map(int, input().split())
B1, C1 = map(int, input().split())

print(solve(B0, C0, B1, C1))