#include<bits/stdc++.h>
using namespace std;

int main()
{
	int a,b;
	while(scanf("%d %d",&a,&b) != EOF)
	{
		if(a > 0)
		{
			b = -b;
		}
		else
		{
			b = b*2;
		}
		
		if(b%2 != 0)
		{
			if(a*b < 0)
					a = -a;
		}
		else
		{
			if(a*b > 0)
				a = -a;
		}
		printf("%d\n",a-b);
	}
	return 0;
}