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