a = input()
b = input()
if len(a) > len(b):
    b = "0" * (len(a) - len(b)) + b
elif len(a) < len(b):
    a = "0" * (len(b) - len(a)) + a

ans = ""
for ca, cb in zip(a, b):
    ans += str(int(ca) ^ int(cb))

print(int(ans, 2))