#include<iostream>
#include<cmath>
#include<cstdlib>
using namespace std;

int main()
{
	int a,b;
	cin >> a >> b;
	if (a>0)
		b=-b;
	else 
		b*=2;
	if (abs(b)%2==1)
		a*=a*b < 0 ? -1:1;
	else
		a*=a*b < 0 ? 1:-1;
	cout << a-b << endl;
}