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