#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

int main() {
    int x, y;
    cin >> x >> y;
    if((x+y) % 2 != 0 && x != 0 && y != 0) {
        cout << "-1\n";
        return 0;
    } else if(x == y) {
        cout << "0\n";
        return 0;
    }
    int times = 0;
    deque<pair<int, int>> cands;
    cands.push_back(make_pair(x, y));
    while(true) {
        times++;
        int limit = cands.size();
        rep(i, limit) {
            pair<int, int> cand = cands.front();
            cands.pop_front();
            if(cand.first+cand.second == cand.first-cand.second) {
                cout << times << "\n";
                return 0;
            }
            cands.push_back(make_pair(cand.second, cand.first));
            cands.push_back(make_pair(cand.first+cand.second, cand.first-cand.second));
        }
    }
}