#include<stdio.h>

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