#include<stdio.h>
#include<math.h>
int main(){
	int a,b,t;
	scanf("%d %d",&a,&b);
	if(a>0)
	b=-b;
	else
	b=b*2;
	if(abs(b)%2==1&&a*b<0){
		a=-a;
	}
	else if(abs(b)%2==0&&a*b>0){
		a=-a;
	}
	t=a-b;
	printf("%d",t);
	
}