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.)

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

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

-----Output-----
Compute f(A, B) and print it.

-----Sample Input-----
2 4

-----Sample Output-----
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.

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