#include<iostream>
#include<vector>
#include<bitset>
#include<algorithm>
#include<cmath>
#include<string>
using namespace std;
int main(){ 
    int X,Y;
    cin >> X >> Y;
    if(X==Y){
        cout << "0\n";
        return 0;
    }
    if(X!=0&&Y!=0){
        cout << "-1\n";
        return 0;
    }
    if(Y!=0)    cout << "2\n";
    else    cout << "1\n";
    return 0;
}