#include<stdio.h>

int main()
{
	int a,b,c,d;
	scanf("%d%d",&a,&b);
	if(a > 0)
	b = -1 * b;
	else
	b = b * 2;
	c = b % 2;
	d = a * b;
	if((c == 1 || c == -1) &&  d < 0)
	a = -1 * a;
	if(c == 0 && d > 0)
	a = -1 * a;
	
	printf("%d",a - b);
	return 0;
}