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

return 0;
}