#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define endl '\n'
typedef pair<int, int> PII;
const int N = 1e5 + 10;
const int mod = 1e9 + 7;
const int INF = 0x3f3f3f3f;
int T;
int x, y, p, qq;
struct node
{
    int d, pos, s, w;
};
int f[2][105][105], ans = 1e9;
void solve()
{
    // code
    cin >> x >> y >> p >> qq;
    queue<node> q;
    memset(f, -1, sizeof f);
    q.push(node{0, 0, x, y});
    f[0][x][y] = 0;
    while (q.size())
    {
        auto t = q.front();
        int d = t.d;
        int pos = t.pos;
        int s = t.s;
        int w = t.w;
        q.pop();
        int ns = x - s;
        int nw = y - w;
        for (int i = min(p, s + w); i >= 0; i--)
        {
            for (int j = min(i, s); j >= max(0, i - w); j--)
            {
                int ww = i - j;
                int ls = s - j;
                int lw = w - ww;
                int rs = ns + j;
                int rw = nw + ww;
                if ((ls == 0 || ls + qq >= lw) && f[pos ^ 1][rs][rw] == -1)
                {
                    f[pos ^ 1][rs][rw] = d + 1;
                    q.push(node{d + 1, (pos ^ 1), rs, rw});
                }
            }
        }
    }
    for (int i = 0; i <= y; i++)
    {
        ans = min(ans, f[1][x][i]);
    }
    if (ans != 1e9)
        cout << ans << '\n';
    else
        cout << -1 << '\n';
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int T = 1;
    // cin >> T;
    while (T--)
    {
        solve();
    }
    return 0;
}