#include<stdio.h>
#include<iostream>
#include<cmath>
using namespace std;
int main(){
	int a, b;
	cin >> a >> b;
	if (a > 0)
		b *= -1;
	else
		b *= 2;
	if (abs(b) % 2 == 1){
		if (b < 0)
			a = abs(a)*(-1);
		else
			a = abs(a);
	}
	else{
		if (b < 0)
			a = abs(a);
		else
			a = abs(a)*-1;
	}
	cout << a - b << endl;
	return 0;
}