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
ans = 0
for i in range(33, -1, -1):
    if 1 & (x >> i) and 1 & (y >> i):
        ans = max(ans, 2 ** i - 1)
print(max(ans, min(x, y, x ^ y)))