#include<iostream>
#include<cstdio>
#include<iomanip>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
int main() {
	int a, b;
	cin >> a >> b;
	if(a > 0)
		b = -b;
	else
		b *= 2;
	if(abs(b) % 2 == 1) {
		if((b < 0 && a > 0) || (b > 0 && a < 0))
			a *= -1;
	}
	else {
		if((b < 0 && a < 0) || (b > 0 && a > 0))
			a *= -1;
	}
	cout << a - b;
	return 0;

}