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