A, B = map(int, input().split())
for i in range(50, -1, -1):
    a = A >> i
    b = B >> i
    if a == 1 and b == 1:
        ans = max(0, 2 ** i - 1)
        print(ans)
        exit()
    elif a == 1:
        print(B & (2 ** i - 1))
        exit()
    elif b == 1:
        print(A & (2 ** i - 1))
        exit()