A = input()
B = input()
N = max(len(A),len(B))
ans = 0
for i in range(1,N+1):
    if i <= len(A):
        a = A[-i]
    else:
        a = "0"
    if i <= len(B):
        b = B[-i]
    else:
        b = "0"
    #print(a,b)
    if a == b:
        continue
    else:
        ans += 2**(i-1)
print(ans)