a = input()
b = input()
if len(a) < len(b):
    a = a.zfill(len(b))
elif len(a) > len(b):
    b = b.zfill(len(a))

ans = ""
for i in range(len(a)):
    if a[i] == b[i]:
        ans = ans + "0"
    else:
        ans = ans + "1"
print(int(ans, 2))