#include<iostream>
#include<cmath>
using namespace std;
int main (){
	int a,b;
	int c;
	cin>>a>>b;
	c=a;
	if(c>0){
		b=b*-1;
	}
	else b*=2;
	if(abs(b)%2!=0){
		if(a*b<0)
			a=a*-1;
	}
	else {
			if(a*b>0){
				a=-1*a;

			}
	}

	cout<<a-b<<endl;
}