#include<iostream>
#include<cstring>
#include<vector>
#include<queue>
#include<array>
using namespace std;
using LL = long long;
int d[105][105][2];

int main(){

#ifdef LOCAL
    freopen("data.in", "r", stdin);
    freopen("data.out", "w", stdout);
#endif

    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(0);

    memset(d, -1, sizeof d);
    int x, y, p, q;
    cin >> x >> y >> p >> q;
    queue<array<int, 3> > que;
    que.push({x, y, 0});
    d[x][y][0] = 0;
    while(!que.empty()){
        auto [a, b, c] = que.front();
        que.pop();
        // cout << a << ' ' << b << ' ' << c << ' ' << d[a][b][c] << '\n';
        if (c == 0){
            for(int i = 0; i <= a && i <= p; i++){
                for(int j = 0; j <= b && i + j <= p; j++){
                    if (b - j - (a - i) > q && a - i > 0) continue;
                    if (d[a - i][b - j][1] == -1){
                        d[a - i][b - j][1] = d[a][b][c] + 1;
                        que.push({a - i, b - j, 1});
                    }
                }
            }
        }
        else{
            int aa = x - a, bb = y - b;
            for(int i = 0; i <= aa && i <= p; i++){
                for(int j = 0; j <= bb && i + j <= p; j++){
                    if (bb - j - (aa - i) > q && aa - i > 0) continue;
                    if (d[i + a][j + b][0] == -1){
                        d[i + a][j + b][0] = d[a][b][c] + 1;
                        que.push({i + a, j + b, 0});
                    }
                }
            }
        }
    }
    const int INF = 1e9;
    int ans = INF;
    for(int i = 0; i <= y; i++){
        if (d[0][i][1] != -1){
            ans = min(ans, d[0][i][1]);
        } 
    }
    if (ans > INF / 2) ans = -1;
    cout << ans << '\n';

}