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