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()

if a > b:
    a, b = b, a
y = 0
x = 0
for i in range(0, 33):
    if 2 ** i <= b:
        y = 2 ** i

for i in range(0, 33):
    if 2 ** i - 1 <= a:
        x = 2 ** i - 1
ans = min(a, b, x, y, x ^ y)
y = 0
x = 0
for i in range(0, 33):
    if 2 ** i - 1 <= b:
        y = 2 ** i - 1

for i in range(0, 33):
    if 2 ** i <= a:
        x = 2 ** i

ans = max(ans, min(a, b, x, y, x ^ y))

print(ans)