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

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