#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define ps push
#define in insert
#define f first
#define s second
#define nl cout<<"\n"
#define ca(v) for(auto i:v) cout<<i<<" ";
#define cbit(x) __builtin_popcount(x)
#define gcd(a, b) __gcd(a, b)
#define lcm(a, b) (a*b/gcd(a, b))
int xm[4] = {-1, 1, 0, 0};
int ym[4] = {0, 0, -1, 1};
const int MOD = 1e9 + 7;
const int MAXN = 5e5 + 5;
const ll POW = 9973;

#define ld long double

pair<ld, ld> eval(ld m, ld h, ld a, ld w){
    // cout<<m*m*w + (h*h-m*m) * a <<" "<<w * m + a * (h - m)<<"\n";
    return {((m*m*w) + ((h*h-m*m) * a)), (w * m + a * (h - m))};
    // return ((m*m*w) + ((h*h-m*m) * a)) / (w * m + a * (h - m));
}
// bool comp(pair<ll,ll> a, pair<ll,ll> b){
//     return a.f * b.s <= b.f * a.s;
// }
bool comp(pair<ld,ld> a, pair<ld,ld> b){
    return a.f * b.s <= b.f * a.s;
}
int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0);
    ld h, R, a, w;
    cin>>h>>R>>a>>w;
    // h *= 10000000;
    ld l = 0;
    ld r = h;
    while(r - l > 1e-7){
        ld diff = (r-l)/3;
        ld m = l + diff;
        ld mp1 = l + 2*diff;
        // cout << "Z"<< m << " " << mp1<<endl;
        // cout<<m<<" "<<mp1<<"\n";
        // cout<<eval(m, h, a, w)<< " "<<eval(mp1, h, a, w)<<"\n";
        if(comp(eval(m, h, a, w), eval(mp1, h, a, w))){
            // l = m;
            r=mp1;
        }
        else{
            // cout<<"E";
            // r = mp1;
            l=m;
        }
    }
    cout << setprecision(9);
    cout<<l<<endl;
}