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