#include<stdio.h>
#include<math.h>
/*int main(){
	int T,i,m;
	double sum,a;
	while(~scanf("%d",&T)){
		sum=0;
		for(i=1;i<=T;i++){
			scanf("%lf",&a);
			if(a>0)
				sum+=a/2.0;
			if(a<=0)
				sum+=a;
			if(sum<0)
				sum+=1;
		}
		m=ceil(sum);
		printf("%d\n",m);
	}
}*/


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