#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(b%2==1||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);
}