#include <cstdio>
#include <cstring>
#include <string>
#include <map>
#include <queue>
#include <stack>
#include <algorithm>　
using namespace std;
const int inf = 0x3f3f3f3f;
#define ll long long
#define pi 3.1415926897932384626
int i, j, k;
int m ,n;
int main() {
	int a,b;
	scanf("%d %d",&a,&b);
	if(a>0)
		b=-1*b;
	else
		b*=2;
	if((abs(b)%2==1&&b<0&&a>0)||(abs(b)%2==1&&b>0&&a<0))
		a=-1*a;
	else if((abs(b)%2==0&&b>0&&a>0)||(abs(b)%2==0&&b<0&&a<0))
		a=-1*a;
	printf("%d\n",a-b);
	return 0;
}