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