#include <bits/stdc++.h>
#define IOS ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

using namespace std;
using ll = long long;

const int N = 100 + 10;

int f[N][N][2];
using t4 = tuple<int, int, int, int>;

void solve(){
    int X, Y, P, q;
    cin >> X >> Y >> P >> q;
    memset(f, 0x3f, sizeof f);
    f[X][Y][0] = 0; //0左侧
    priority_queue<t4, vector<t4>, greater<t4>> q4;
    q4.push(make_tuple(0, X, Y, 0));
    int t = 0;
    while (!q4.empty()){
        auto [d, x, y, k] = q4.top();
        //if (t++>100) break;
        //cout << d << ' ' <<  x << ' ' << y << ' ' << k << '\n';
        q4.pop();
        if (k == 1){
            if (f[x][y][0] == 0x3f3f3f3f){
                f[x][y][0] = d + 1;
                q4.push(make_tuple(d + 1, x, y, 0));
            }
        }else{
            for (int i = 0; i <= min(Y, P); i ++ ){
                int ty = i;
                int tx = min(P - i, x);
                if (y - ty - (x - tx) > q && x - tx > 0) continue;
                if (f[x-tx][y-ty][1] != 0x3f3f3f3f) continue;
                f[x-tx][y-ty][1] = d+1;
                q4.push(make_tuple(d+1, x-tx, y-ty, 1));
            }
        }
    }
    int mi = 0x3f3f3f3f;
    for (int j = 0; j <= Y; j ++ ) mi = min(mi, f[0][j][1]);
    if (mi == 0x3f3f3f3f) mi = -1;
    cout << mi;
}

signed main(){
    IOS;
    int t = 1;
//		cin >> t;
    while (t -- ){
        solve();
    }
    return 0;
}