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

//#define int long long
#define rep(i,n) for(int (i)=0;(i)<(int)(n);(i)++)
#define rept(i,n) for(int (i)=0;(i)<=(int)(n);(i)++)
#define reps(i,s,n) for(int (i)=(s);(i)<(int)(n);(i)++)
#define repst(i,s,n) for(int (i)=(s);(i)<=(int)(n);(i)++)
#define repr(i,n) for(int (i)=(n);(i)>=0;(i)--)
#define each(itr,v) for(auto (itr):(v))
#define all(c) (c).begin(),(c).end()
#define pb push_back
#define mp(x,y) make_pair((x),(y))
#define fi first
#define se second
#define chmin(x,y) x=min(x,y)
#define chmax(x,y) x=max(x,y)
#define ln '\n'
#define dbg(x) cout<<#x" = "<<(x)<<ln

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vector<int> > mat;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

const int inf = (int)1e9;
const ll linf = (ll)1e18;
const int mod = (int)(1e9+7);
const int dx[] = {0, 1, 0, -1};
const int dy[] = {1, 0, -1, 0};
const int ddx[] = {0, 1, 1, 1, 0, -1, -1, -1};
const int ddy[] = {1, 1, 0, -1, -1, -1, 0, 1};
const double eps = 1e-10;

struct oreno_initializer {
	oreno_initializer() {
		cin.tie(0);
		ios::sync_with_stdio(0);
	}
} oreno_initializer;

// ━━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…
// .｡.:( ^ω^)・ﾟ＋.｡.:( ^ω^)・ﾟ＋.｡.:( ^ω^)・ﾟ＋.｡.:( ^ω^)・ﾟ＋.｡.:( ^ω^)・ﾟ＋
// ・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・‥…━━━☆・

ll x, y, r;

signed main() {
	/*
	rep(i,100) rep(j,100) {
			x = i, y = j;
			cout << x << ' ' << y << ' ';
			//cin >> x >> y;
			while (x != y && r <= 1000000) {
				if (x < y) swap(x, y), r++;
				else {
					ll xx = x + y, yy = x - y;
					x = xx, y = yy;
					r++;
				}
				if (abs(x) > inf || abs(y) > inf) {
					//cout << -1 << ln;
					//return 0;
					break;
				}
			}
			if (r == 1000000 || x!=y) cout << -1 << ln;
			else cout << r << ln;
			r = 0;
		}
	 */
	cin >> x >> y;
	if (x==y) r = 0;
	else if (y==0) r = 1;
	else if (x==0) r = 2;
	else r = -1;
	cout << -1 << ln;
}