#include<bits/stdc++.h>

#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e2 + 5;
const int mod = 1e9 + 7;
const int oo = 1e9 + 7;

int x, y, p, q;

int f[maxN][maxN][2];

struct TState {
    int sheep, wolf;
    bool side;
};

void ReadInput()
{
    cin >> x >> y >> p >> q;

    //memset(f, -1, sizeof(f));

    fill(&f[0][0][0], &f[0][0][0] + maxN * maxN * 2, -1);
}

int dp(const int &i, const int &j, const bool &side)
{

    if(i == x && side) return 0;


    int &res = f[i][j][side];



    if(res != -1) return res;

    res = oo;
    if(i == 2 && j == 1 && !side)
    {
        // cout << dp(1, 1, 1);exit(0);
    }
    // if(side) return dp(x - i, y - j, !side) + 1;

    for(int a = 0; a <= i; a++)
    {
        for(int b = j; b >=0; b--)
        {
            if(a + b > p) continue;
            // cerr << "check " << i << ' ' << j << ' ' << side << ' ' << a << ' ' << b << ' ' << (j - b > i - a + q && i - a > 0) << '\n';
            if(j - b > i - a + q && i - a > 0) continue;

            //if(a + b == 0 && !side) continue;
            // cerr << i << ' ' << j << ' ' << side << " ==>> " << ' ' << x - (i - a) << ' ' << y - (j - b) << ' ' << !side << ' ' << f[x - (i - a)][y - (j - b)][!side] << '\n';
            int nxt_state = dp(x - (i - a), y - (j - b), !side);
            if(i == 2 && j == 1 && !side)
            {
               // cerr << dp(1, 0, 1) << " ";
                //cerr << x - (i - a) << " " << " " << y - (j - b) << " " << nxt_state << '\n';
            }
            // if(nxt_state >= oo) continue;
            res = min(res, nxt_state + 1);
        }
    }
    if(i == 2 && j == 1 && !side)
    {
       // cerr << res;
        //exit(0);
    }
    //cerr << i << ' ' << j << ' ' << side << ' ' << res << '\n';

    return res;
}

void bfs() {
    queue<TState> qu;
    qu.push({x, y, false});
    f[x][y][false] = 0;
    while(qu.size()) {
        TState u = qu.front();
        qu.pop();
        int cur_depth = f[u.sheep][u.wolf][u.side];
        //cerr << u.sheep << ' ' << u.wolf << ' ' << u.side << ' ' << cur_depth << '\n';
        for(int a = 0; a <= u.sheep; a++) {
            for(int b = 0; b <= u.wolf; b++) {
                if(a + b > p) break;
                int numSheepLeft = u.sheep - a;
                int numWolfLeft = u.wolf - b;
                if(numWolfLeft > numSheepLeft + q && numSheepLeft > 0) continue;
                TState v = {x - numSheepLeft, y - numWolfLeft, !u.side};
                if(f[v.sheep][v.wolf][v.side] != -1) continue;
                qu.push(v);
                f[v.sheep][v.wolf][v.side] = 1 + cur_depth;
            }
        }
    }
}

void Solve()
{
    bfs();
    int res = oo;
    for(int i = 0; i <= y; i++) {
        if(f[x][i][true] != -1) res = min(res, f[x][i][true]);
    }
    if(res == oo) cout << -1;
    else cout << res;
}
#define taskname "C"
int32_t main()
{
    if (fopen(taskname ".inp", "r"))
    {
        freopen(taskname ".inp", "r", stdin);
        freopen(taskname ".out", "w", stdout);
    }
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int T = 1;
    //cin >> T;
    for(int itest=1; itest<=T; itest++)
    {
        ReadInput();
        Solve();
    }
}