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