import sys
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
INF = 2 ** 63 - 1
mod = 998244353

a, b = mi()

x, y = a, b

for i in range(33, -1, -1):
    if 1 & (x >> i) and 1 & (y >> i):
        ans1 = min(2 ** i - 1, y, (2 ** i - 1) ^ y)
        ans2 = min(x, 2 ** i - 1, x ^ (2 ** i - 1))
        print(max(ans1, ans2))
        exit()
print(min(x, y, x ^ y))