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