Untitled

#include <iostream>
using namespace std;

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

}