a,b=map(int,input().split())
ans=0
for _ in range(2):
    for i in range(33):
        x=1<<i
        if x<=a:
            y=0
            for j in range(i-1,-1,-1):
                if y|(1<<j)<=b:
                    y|=1<<j
            ans=max(ans,y)   
    a,b=b,a
print(ans)