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

}