#include<stdio.h>
#include<math.h>
#include<stdlib.h>
int main(){
	int a,b;
	scanf("%d%d",&a,&b);
	if(a>0){
		b *= -1;
	}else{
		b*=2;
	}
	if(abs(b)%2==1){
		if(b>0){
			a = abs(a);
		}else if(b<0){
			a = abs(a) * -1;
		}
	}else{
		if(b<0){
			a = abs(a);
		}else if(b>0){
			a = abs(a) * -1;
		}
	}
	printf("%d\n",a-b);
}