#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

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



}