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

#define ll long long 
#define lll __int128
#define INF 0x3f3f3f3f
#define LNF 0x3f3f3f3f3f3f3f3fll
#define MOD 998244353
#define pii pair<int, int>
#define ld long double
#define fi first
#define se second
#define all(a) a.begin(), a.end()

#define N 110


int main() {
#ifdef TEST
    freopen("zz.in", "r+", stdin);
#endif
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cout << setprecision(18);

    int x, y, p, q; cin >> x >> y >> p >> q;    
    int sx = 0, sy = 0;
    y -= sy;

    int tx = 0, ty = 0;
    int d = INF, stp = 0, f = 1;

    auto trans = [&](int& x, int& y, int d) {
        x += d, y -= d;
    };

    while (stp < 10) {
        f &= p-sx-sy>=y-(x+q);
        trans(sy, y, max(0, y-(x+q)));
        trans(sx, x, min(p-sx-sy, max(0, x-(y-q))));
        d = min((p-sx-sy)/2, min(x, y));
        trans(sx, x, d);
        trans(sy, y, d);
        if (p-sx>=x) {
            trans(y, sy, sy);
            trans(sx, x, x);
        }
        ++ stp;

        trans(tx, sx, sx);
        trans(ty, sy, sy);
        if (x == 0) break;

        if (tx) {
            f &= p-sx-sy>=ty-(tx+q);
            trans(sy, ty, max(0, ty-(tx+q)));
        }
        ++ stp;
    }

    cout << (!f || stp == int(1e5) ? -1 : stp) << '\n';
}   

// 3 3
// 2 2