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


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

	return 0;
}