#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<string>
using namespace std;
int const maxn=110;
int a,b,c,d,e,cnt,sum;
int i,j;
int main(){
	scanf("%d %d",&a,&b);
	if(a>0)
	b*=-1;
	else b*=2;
	if(abs(b)%2==1){
		if((a>0&&b<0)||(a<0&&b>0))
		a*=-1;
	}
	else {
		if((a>0&&b>0)||(a<0&&b<0))
		a*=-1;
	}
	printf("%d\n",a-b);
	return 0;
}