题目描述

Let f(A,B) be the exclusive OR of A,A+1,...,B. Find f(A,B).
What is exclusive OR?
Constraints
All values in input are integers.
0≤A≤B≤1012

输入

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

输出

Compute f(A,B) and print it.

样例输入 Copy

2 4

样例输出 Copy

5

提示

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

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll f(ll x)
{
    if (x % 4 == 0)
        return x;
    if (x % 4 == 1)
        return 1;
    if (x % 4 == 2)
        return x + 1;
    return 0;
}
int main()
{
    ll A, B;
    cin >> A >> B;
    cout << (f(B) ^ f(A - 1)) << endl;
    return 0;
}