A = list(input())
B = list(input())

A.reverse()
B.reverse()

while len(A) < len(B):
    A.append(0)
while len(B) < len(A):
    B.append(0)

ans = 0

A.reverse()
B.reverse()

for i,j in zip(A,B):

    ans *= 2
    ans += int(i) ^ int(j)

print (ans)