#include<cstdio>
#include<cstring>
#include<cmath>
#include<map>
#include<set>
#include<string>
#include<algorithm>
#define ll long long 
using namespace std;
const int maxn = 200010;
const int inf = 0x3f3f3f3f;
int  x, y, n, k, m;
int a, b, c, d, e;
int main()
{
	while (scanf("%d %d", &a, &b) != EOF) 
	{
		if (a > 0)
			b *= -1;
		else
			b *= 2;
		if (abs(b) % 2)
		{
			if ((b < 0 && a>0) || (b > 0 && a < 0))
				a *= -1;
		}
		else 
		{
			if ((a > 0 && b > 0) || (a < 0 && b < 0))
				a *= -1;
		}
		printf("%d\n", a - b);


	}
	return 0;
}