#include <bits/stdc++.h>
#define lowbit(x) x&(-x)
using namespace std;
using i64 = long long;
using pii = std::pair<int, int>;
constexpr int mod = 998244353;
constexpr int MAXN_32 = 2e9;
constexpr i64 MAXN_64 = 1e18;

template <typename T>
void debug(T x) {
    cerr << x << "\n";
}

template <typename T, typename... Args>
void debug(T x, Args... args) {
    cerr << x << " ";
    debug(args...);
}

struct node {
    int x, y, id;
};

void solve() {
    int x, y, p, q;
    cin >> x >> y >> p >> q;
    vector G(x + 1, vector(y + 1, vector(2, vector<node>())));

    for(int i = x; i >= 0; i--) {
        for(int j = y; j >= 0; j--) {
            for(int k = i; k >= 0; k--) {
                for(int l = j; l >= 0; l--) {
                    int sum = i + j - k - l;
                    if(sum > p) continue;
                    if(k && k + q < l) continue;
                    // debug(i, j, k, l);
                    G[i][j][0].emplace_back(x - k, y - l, 1);
                    G[i][j][1].emplace_back(x - k, y - l, 0);
                }
            }
        }
    }

    vector dis(x + 1, vector(y + 1, vector(2, 0ll)));
    queue <node> qq;
    qq.emplace(x, y, 0);
    dis[x][y][0] = 1;
    while(!qq.empty()) {
        auto [nx, ny, nid] = qq.front();
        qq.pop();
        for(auto [dx, dy, id] : G[nx][ny][nid]) {
            if(dis[dx][dy][id]) continue;
            dis[dx][dy][id] = dis[nx][ny][nid] + 1;
            qq.emplace(dx, dy, id);
        }
    }

    i64 ans = MAXN_32;

    for(int i = 0; i <= y; i++) {
        if(dis[x][i][1]) ans = min(ans, dis[x][i][1] - 1);
    }

    if(ans == MAXN_32) cout << "-1\n";
    else cout << ans << '\n';
}

int main() {
    std::cin.tie(nullptr)->sync_with_stdio(false);
    int t = 1;
    // std::cin >> t;
    while(t--) solve();
    return 0;
}