#include <iostream>
#include <vector>
#include <climits>
#include <algorithm>
#include <cmath>
#include <map>
#include <set>
#include <string>
#include <bitset>
#include <utility>
#include <numeric>
#include <queue>
#include <stack>

using ll = long long;
using namespace std;

constexpr int MOD = 1e9 + 7;
constexpr ll MOD_LL = ll(1e9) + 7;

int main(void) {
	ll a, b;
	cin >> a >> b;
	
	if( b == 0 ) {
		cout << 0 << endl;
	} else if( b != 0 && a == -1 ) {
		cout << 2 << endl;
	} else {
		cout << -1 << endl;
	}
	
	return 0;
}