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