#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=105,INF=1<<30;

int dis[MAX][MAX][2];

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    int x,y,p,q;cin>>x>>y>>p>>q;
    for(int i=0;i<MAX;i++) for(int j=0;j<MAX;j++) dis[i][j][0]=dis[i][j][1]=INF;
    queue<tuple<int,int,int>> Q;
    Q.push({x,y,0});
    dis[x][y][0]=0;
    
    while(!Q.empty()){
        auto [a,b,qq]=Q.front();Q.pop();
        //cout<<a<<" "<<b<<" "<<qq<<" "<<dis[a][b][qq]<<endl;
        for(int s=0;s<=a;s++){
            for(int t=0;t<=b;t++){
                if(s+t>p) break;
                int xx=a-s,yy=b-t;
                //cout<<"! "<<s<<" "<<t<<" "<<xx<<" "<<yy<<endl;
                if(xx&&xx+q<yy) continue;
                xx=x-xx;
                yy=y-yy;
                //cout<<"! "<<s<<" "<<t<<" "<<xx<<" "<<yy<<endl;
                if(chmin(dis[xx][yy][qq^1],dis[a][b][qq]+1)) Q.push({xx,yy,qq^1});
            }
        }
    }
    
    int ans=INF;
    
    for(int t=0;t<=y;t++) chmin(ans,dis[x][t][1]);
    
    if(ans==INF) ans=-1;
    cout<<ans<<endl;
}