#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) {
    return (ull)rng() % B;
}
inline double time() {
    return static_cast<long double>(chrono::duration_cast<chrono::nanoseconds>(chrono::steady_clock::now().time_since_epoch()).count()) * 1e-9;
}

bool used[2][101][101];
int dp[2][101][101];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int x,y,p,q; cin >> x >> y >> p >> q;
    using P = pair<int,int>;
    queue<pair<int,P>> que;
    auto push = [&](int t, int x, int y, int d) -> void {
        if (!used[t][x][y]) {
            used[t][x][y] = true;
            dp[t][x][y] = d;
            que.push({t, {x, y}});
        }
    };
    push(0, x, y, 0);

    int res = -1;
    while (que.size()) {
        auto pp = que.front(); que.pop();
        int t = pp.first;
        int xx = x, yy = y;
        if (t == 0) {
            xx = pp.second.first, yy = pp.second.second;
        } else {
            xx -= pp.second.first, yy -= pp.second.second;
        }
        int val = dp[t][pp.second.first][pp.second.second];
//        cout  << t << " " << xx << " " << yy << " " << val << endl;
        if (t == 1 and xx == x) {
            res = val;
            break;
        }
        for (int i = 0; i <= p; ++i) {
            for (int j = 0; j <= min(i,xx); ++j) {
                int k = i-j;
                if (k < 0) continue;
                if (k > yy) continue;
                int nx = xx-j, ny = yy-k;
                if (nx+q < ny and nx) continue;

                if (t == 0) {
                    push(1, nx, ny, val+1);
                }
                else {
                    push(0, x-nx, y-ny, val+1);
                }
            }
        }
    }
    cout << res << endl;
}