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