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

	if(abs(b)%2==1) {
		if(b!=0) a=b/abs(b)*abs(a);
	} else if(abs(b)%2==0){
	if(b!=0) a=-b/abs(b)*abs(a);}
	printf("%d\n",a-b);
}