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

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

}