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

if A == 0 and B == 0:
    print(0)
    exit()

max_ = max(A,B)
min_ = min(A,B)

maxbin = bin(max_)[2:]
minbin = bin(min_)[2:]

if len(maxbin) == len(minbin):
    if len(minbin)-1 == 0:
        print(0)
    else:
        tmp = "1"*(len(minbin)-1)
        ans = int(tmp,2)
        print(ans)
else:
    print(min_)