#include <bits/stdc++.h>
#define MODNum 1000000007
#define REP(type, i, a, b) for( type i = a; i < b; i++ )
typedef long long ll;

using namespace std;

int main (void) {
    ll A, B, ans;
    cin >> A >> B;
    if ( B == 0 ) ans = 1;
    else{
        if ( B * A + B == 0 ) ans = 2;
        else ans = -1;
    }
    cout << ans << endl;
    return 0;
}