#include <bits/stdc++.h>

#define pb push_back
#define fi first
#define se second

using namespace std;

int n, m, p, q;
int to(int x, int y, int a)
{
    return a*(n+1)*(m+1) + x*(m+1) + y;
}
array<int, 3> to(int x)
{
    return {x/(m+1)%(n+1), x%(m+1), x/(m+1)/(n+1)};
}

vector<int> edges(int a)
{
    int x = to(a)[0];
    int y = to(a)[1];
    int b = to(a)[2];
    vector<int> res;
    if (b == 0)
    {
        for (int i=0; i<=x; i++)
            for (int j=0; j<=y; j++)
                if (i+j <= p)
                    if (y-j <= x-i+q || x-i==0)
                        res.pb(to(x-i, y-j, 1));
    }
    else
    {
        for (int i=0; i<=n-x; i++)
            for (int j=0; j<=m-y; j++)
                if (i+j <= p)
                    if (m-y-j <= n-x-i+q || n-x-i==0)
                        res.pb(to(x+i, y+j, 0));
    }
    return res;
}

int d[1000000];

main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin>>n>>m>>p>>q;

    memset(d, 255, sizeof(d));
    int s = to(n, m, 0);
    queue<int> q;
    q.push(s);
    d[s] = 0;

    while (!q.empty())
    {
        int v = q.front();
        q.pop();
//        cout<<to(v)[0]<<" "<<to(v)[1]<<" "<<to(v)[2]<<" "<<d[v]<<"\n";
        for (int i : edges(v))
            if (d[i] == -1)
        {
            d[i] = d[v] + 1;
            q.push(i);
            if (to(i)[0] == 0)
            {
                cout<<d[i]<<"\n";
                exit(0);
            }
        }
    }
    cout<<"-1\n";
}