#include<stdio.h>
#include<math.h>
int main(void){
	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)){
			a=-a;
		}
	}else{
		if((a<=0&&b<=0)||(a>=0&&b>=0)){
			a=-a;
		}
	}
	printf("%d",a-b);
	return 0;
}