#include<stdio.h>

int main()
{
	int a,b;
	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;
    printf("%d\n",a-b);
	return 0;
}