import sys
read = sys.stdin.buffer.read

A,B = map(int,read().split())

x = 1
for _ in range(40):
    a = (A & 1); b = (B & 1)
    if (a,b) == (0,1):
        x *= 2
    if (a,b) == (1,0):
        x = 0
        break
    A >>= 1; B >>= 1

if A == B:
    x += 1
print(x // 2)