Untitled

#include <iostream>

using namespace std;

int main() {
	int a, b;
	cin >> a >> b;

	if (a % 2 == 0 && a > 0) {
		if (b % 2 != 0 && b < 0) {
			cout << a - b;
		}
	}
	else if (b % 2 == 0 && b > 0) {
		if (a % 2 != 0 && a < 0) {
			cout << b - a;
		}
	} 
	else cout << "NO";
}