#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
#define DUMP(x) cout << #x << " = " << (x) << endl;
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define IFOR(i, m, n) for (ll i = n - 1; i >= m; i--)
#define REP(i, n) FOR(i, 0, n)
#define IREP(i, n) IFOR(i, 0, n)
#define FOREACH(x, a) for (auto&(x) : (a))
#define ALL(v) (v).begin(), (v).end()
#define SZ(x) ll(x.size())

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