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

int main() {
	int a, b;
	scanf("%d %d", &a, &b);
	if (a > 0) {
		b = -b;

	}
	else {
		b = b * 2;
	}

	int flagb ;
	if (b == 0) {
		flagb = 1;
	}
	else {
		flagb = b / abs(b);
	}
	int flaga;
	if (a == 0) {
		flaga = 1;
	}
	else {
		flaga = a / abs(a);
	}
	if (abs(b) % 2 == 1) {
		if (flaga != flagb) {
			a = a * -1;
		}
	}
	else {
		if (flaga == flagb) {
			a = a * -1;
		}
	}
	printf("%d", a - b);
}