#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=144499999999994;
ll mod=998244353;
int main(){
    ll a,b;
    cin >> a  >> b;
    if (a==-1||b==0)
    {
        if (b!=0)
        {
            cout << 2 << endl;
        }else{
            cout << 1 << endl;
        }
        
    }else{
        cout << -1 << endl;
    }
    
}