A, C = list(map(int, input().split()))
bA = []
bC = []
while True:
    if A == 0 and C == 0:
        break
    else:
        bC.append(C % 2)
        bA.append(A % 2)
        A //= 2
        C //= 2

bB = [(ba==1 and bc==0) or (ba==0 and bc==1) for ba, bc in zip(bA, bC)]

tmp = 1
B = 0
for bb in bB:
    if bb:
        B += tmp
    tmp *= 2

print(B)