A,B=(int(x) for x in input().split())
a=list(bin(A))[2:][::-1]
b=list(bin(B))[2:][::-1]

for i in range(10):
    a.append(0)
    b.append(0)

res=[]
for i,j in zip(a,b):
    if i == j:
        res.append(0)
    else:
        res.append(1)

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

print(ans)