#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;

int a, b, sum;
int main() {
	cin >> a >> b;
	if (a > 0)b *= -1;
	else b *= 2;
	if (b % 2 == 0) {
		if (a*b > 0)
			a *= -1;
	}
	else {
		if (a*b < 0)
			a *= -1;
	}
	sum = a - b;
	printf("%d", sum);
}