#include <iostream>

int main(void){
  using namespace std;
  int a,b;
  cin >> a >> b;
  //cout << a << b << endl;
  if(a==-1)cout << 2 << endl;
  if(b==0)cout << 1 << endl;
  if((a!=-1)&&(b!=0)) cout << -1 << endl;
  return 0;    
}