#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <math.h>

using namespace std;

#define REP(i,n)	for(int i=0;i<(n);++i)
#define REPS(i,s,t)	for(int i=(s);i<(t);++i)

#define INF 		2000000007
#define MOD			1000000007
#define MAX 		100005


typedef unsigned int 			uint;
typedef unsigned long long int	ull;
typedef long long int ll;

//uint dp[MAX];

int main(){
	int X,Y;cin>>X>>Y;

	if(X==Y)
		cout << 0 << endl;
	else if(X==0 || Y==0)
		cout << 2 << endl;
	else if((X+Y)==0)
		cout << 3 << endl;
	else 
		cout << -1 << endl;


	return 0;
}