#include<stdio.h>
#include<stdlib.h>
int main(void){
	int a,b,c;
	scanf("%d%d",&a,&b);
	if(a>0)
	b=-b;
	else{
	b=2*b;}
    if(abs(b)%2!=0)
    	if(a/(b*1.0)<0)
    	a=(-1)*a;
    if(abs(b)%2==0)   
		if(a/(b*1.0)>0){
		a=-a;}
	    c=a-b;
	    printf("%d",c);
		return 0;
}