#include <bits/stdc++.h>
#define REP(i,a,b) for(int i=(a);i<(b);i++)
#define RREP(i,a,b) for(int i=(a);i>=(b);i--)
#define pq priority_queue
#define P pair<int,int>
#define P2 pair<int,P>
#define P3 pair<int,P2>
typedef long long ll; typedef long double ld;
using namespace std;
const int INF=1e9, MOD=1e9+7, around[]={0,1,1,-1,-1,0,-1,1,0,0};
const ll LINF=1e18;
const ld PI=abs(acos(-1));
int a,b;

int main(){
	cin >> a >> b;
	if(a == b){cout << 0 << endl; return 0;}
	if(!a or !b){cout << (!a?2:1) << endl; return 0;}
	if(-a == b){cout << 3 << endl; return 0;}
	cout << -1 << endl;
	return 0;
}