def INT():
    return int(input())


def MI():
    return map(int, input().split())


def LI():
    return list(map(int, input().split()))


A = list(input())
B = list(input())
A = A[::-1]
B = B[::-1]

a = 0
for i in range(len(A)):
    if A[i] == "1":
        a += 2**i

b = 0
for i in range(len(B)):
    if B[i] == "1":
        b += 2**i

print(a ^ b)