#include <bits/stdc++.h>

int main(){
  int64_t a, b; std::cin >> a >> b;

  int ans = -1;

  if(b == 0){
    ans = 1;
  }else if(a == -1){
    ans = 2;
  }
  
  std::cout << ans << "\n";

  return 0;
}