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