#include<cstdio>
#include<iostream>
#include<algorithm>
#include<stdlib.h>
#include<string>
#include<string.h>
#include<math.h>
using namespace std;
const int maxn=110;
int main(){
	int a,b;
	scanf("%d%d",&a,&b);
	if(a>0)b=-b;
	if(a<=0)b=b*2;
	if(abs(b)%2==1){
		if(b>0){
			if(a<0)a=-a;
		}
		if(b<0){
			if(a>0)a=-a;
		}
	}
	if(abs(b)%2==0){
		if(b>0){
			if(a>0)a=-a;
		}
		if(b<0){
			if(a<0)a=-a;
		}
	}
	printf("%d\n",a-b);
}