#include<stdio.h>
#include<math.h>

int main(){
	int a, b;
	scanf("%d %d", &a, &b);
	
	if(a > 0){
		b = -b;
	}else{
		b = 2*b;
	}
	
	if(abs(b)%2 == 1){
		if(b > 0){
			if(a < 0){
				a = -a;
			}
		}else{
			if(a > 0){
				a = -a;
			}
		}
	}else{
		if(b > 0){
			if(a > 0){
				a = -a;
			}
		}else{
			if(a < 0){
				a = -a;
			}
		}
	}
	
	printf("%d\n", a-b);
	
}