#include <iostream>
using namespace std;

int main() {
	int x, y, x2, y2;
	cin >> x >> y;

	int ans = -1;
	if (x == y) {
		ans = 0;
	} else if (x == 0) {
		ans = 2;
	} else if (y == 0) {
		ans = 1;
	}

	cout << ans << endl;
	return 0;
}