#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
int main()
{
   int a,b,p;
   scanf("%d%d",&a,&b);
   if(a>0)
	 b=-1*b;
   if(a<=0)
	   b=b*2;
  if((b%2==1||b%2==-1)&&((b>0&&a<0)||(b<0&&a>0)))
		  a=-1*a;
 if((b%2==0)&&((b>0&&a>0)||(b<0&&a<0)))
	  a=-1*a;
   printf("%d\n",a-b);

}