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