#include<cstdio>
#include<algorithm>
#include<cstring>
using namespace std;
int main(){
	int a,b;
	while(~scanf("%d%d",&a,&b)){
		if(a>0)
			b=-b;
		else
			b*=2;
		if(abs(b)&1){
			if(a*b<0)
				a=-a;
		}
		else{
			if(a*b>0)
				a=-a;
		}
		printf("%d\n",a-b);
	}
}