#include<stdio.h>
int main()
{
	int a,b,sum=0;
	while(scanf("%d %d",&a,&b)!=EOF)
	{
	if(a>0&&b>0)
	{
		if(b%2==1)
			sum=-a+b;
		else
			sum=a+b;
	}
	else if(a>0&&b<=0)
	{
		if(b%2==-1)
			sum=a+b;
		else
			sum=-a+b;
	}
	else if(a<=0&&b>0)
	{
		
			sum=a-2*b;
	}
	else if(a<=0&&b<=0)
	{
		
			sum=-a-2*b;
	}
	printf("%d\n",sum);
	}
}