Problem Statement

Let f(A, B) be the exclusive OR of A, A+1, ..., B. Find f(A, B).

What is exclusive OR?
The bitwise exclusive OR of integers c_1, c_2, ..., c_n (let us call it y) is defined as follows:

• When y is written in base two, the digit in the 2^k'$s place (k \geq 0)$ is 1 if, the number of integers among c_1, c_2, ...c_m whose binary representations have 1 in the 2^k's place, is odd, and 0 if that count is even.

For example, the exclusive OR of 3 and 5 is 6. (When written in base two: the exclusive OR of 011 and 101 is 110.)

Input

Input is given from Standard Input in the following format:
A B

Output

Compute f(A, B) and print it.

Constraints

• All values in input are integers.
• $0 \leq A \leq B \leq 10^{12}$

Sample Input 1

2 4

Sample Output 1

5

2, 3, 4 are 010, 011, 100 in base two, respectively.
The exclusive OR of these is 101, which is 5 in base ten.

Sample Input 2

123 456

Sample Output 2

435

Sample Input 3

123456789012 123456789012

Sample Output 3

123456789012

见题面 Input 部分

见题面 Output 部分