import math
A, B = map(int, input().split())

ans=0
amin=max(2**int(math.log2(A))-10,0)
bmin=max(2**int(math.log2(B))-10,0)
amax=min(amin+20,A+1)
bmax=min(bmin+20,B+1)
#print(amin, amax, bmin, bmax)
for a in range(amin, amax, 1):
    for b in range(bmin, bmax, 1):
        ans1=min(a, b, a^b)
#        print(a,b,a^b)
        if ans<ans1:
            ans=ans1
print(ans)