#include<stdio.h>
#include<math.h>
int main()
{  int a,b,c;
scanf("%d%d",&a,&b);
  if(a<=0)
{
	b=2*b;
	if(b<0) c=-a-b; else c=a-b;
  }
  if(a>0)
  {
	  b=-b;
	  if(abs(b)%2==0)
	  {
		  if(b>0){ a=-a;c=a-b;}
		  else if(b<0){a=a;c=a-b;}
	  }
	  if(abs(b)%2==1)
	  {
		  if(b>0){a=a;c=a-b;}
		  else if(b<0){a=-a;c=a-b;}
	  }
  }
  printf("%d",c);
}