#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
using ll =  long long ;
using P = pair<int,int> ;
using pll = pair<ll,ll>;
const ll INF = 1e18;
const int MOD = 1000000007;

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