#include<bits/stdc++.h>
#define int long long
#define IOS ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
using namespace std;

typedef long double ld;
typedef pair<int,int> pii;
const int N = 2e5+10;

signed main(){
    IOS;
    int x,y,p,q;
    cin>>x>>y>>p>>q;
    if(x+p+q<y){
        cout<<-1<<endl;
    }else{
        int pcnt=(p+q)/2;
        if(!pcnt){
            cout<<x<<endl;
            return 0;
        }
        int ans=x/pcnt;
        ans=ans*2-1;
        cout<<ans<<endl;
    }

    return 0;
}