#include<stdio.h>
#include<math.h>

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