a, c = io.read("*n", "*n")
t = {}
while(a ~= 0 or c ~= 0) do
    if(a % 2 == c % 2) then table.insert(t, 0) else table.insert(t, 1) end
    a, c = math.floor(a / 2), math.floor(c / 2)
end
ret = 0
for k, v in pairs(t) do
    ret = ret + v * math.pow(2, k - 1)
end
print(ret)