Little Girl and Maximum XOR

在区间[l,r]中找出两个数a,b(a <= b),使得a ^ b达到最大

A little girl loves problems on bitwise operations very much. Here's one of them. You are given two integers $ l $ and $ r $ . Let's consider the values of  for all pairs of integers $ a $ and $ b $ $ (l<=a<=b<=r) $ . Your task is to find the maximum value among all considered ones. Expression  means applying bitwise excluding or operation to integers $ x $ and $ y $ . The given operation exists in all modern programming languages, for example, in languages $ C $ ++ and $ Java $ it is represented as "^", in $ Pascal $ — as «xor».

The single line contains space-separated integers $ l $ and $ r $ ( $ 1<=l<=r<=10^{18} $ ). Please, do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64d specifier.

In a single line print a single integer — the maximum value of  for all pairs of integers $ a $ , $ b $ $ (l<=a<=b<=r) $ .

1 2

3

8 16

31

1 1

0