#include<iostream>
#include<cmath>
using namespace std;
int main(){
	int a,b,b1;
	cin>>a>>b;
	if(a>0){
		b=b*(-1);
	}
	else{
		b=b*2;
	}
	if(abs(b)%2==1){
		if(a*b<=0)
		a=-1*a;
	}
	else if(abs(b)%2==0){
		if(a*b>=0)
		a=-1*a;
	}
	cout<<a-b<<endl;
}