#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
ll mod = 1000000007;

ll r(ll x, ll y) {
  if (y == 0) return 1;
  else if (y % 2 == 0) return r(x, y/2) * r(x, y/2) % mod;
  else return x * r(x, (y-1)/2) % mod * r(x, (y-1)/2) % mod;
}

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