# input

x = input().split()

x1 = int(x[0])
x2 = int(x[1])

n = 0

# for

if (x1-x2)%2 == 0:
    n = 2
    while n != -1:
        if  n ^ x1 == x2:
            print(n)
            break
        else:
            n += 2
else:
    n = 1
    while n != -1:
        if  n ^ x1 == x2:
            print(n)
            break
        else:
            n += 2