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