#include<stdio.h>
#include<math.h>

int main(){
	int a,b;
	scanf("%d %d",&a,&b);
	if(a<=0){
		b=2*b;
		if(b>0){
			printf("%d",a-b);
		}
		else{
			a=-1*a;
			printf("%d",a-b);
		}
	}else{
		b=-1*b;
		if(abs(b)%2 == 0){
			if(b>0){
				a=-1*a;
				printf("%d",a-b);
			}
			else{
				printf("%d",a-b);
			}
		}
		else{
			if(b>0){
			printf("%d",a-b);
			}
			else{
				a=-1*a;
				printf("%d",a-b);
			}
		}
	}
	return 0;
}