s = input()
t = input()

if s > t:
    s, t = t, s

while len(s) < len(t):
    s = '0' + s

ans = ''
for i in range(len(s)):
    if s[i] == '1':
        if t[i] == '0':
            ans += '1'
        else:
            ans += '0'
    else:
        if t[i] == '0':
            ans += '0'
        else:
            ans += '1'

z = 0
for i in range(len(ans)):
    z *= 2
    if ans[i] == '1':
        z += 1

print(z)