#include<bits/stdc++.h>
#include<iostream>
#include <iomanip>
#include<math.h>
#include<fstream>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define fi first
#define se second
#define gap ' '
#define abs(x) ((x)>0?(x):-(x))
#define INF 1e18
#define mod 998244353
#define inf 1e9
#define pi 2*acos(0.0)
#include<time.h>
//#define endl '\n'
//#define int ll
#define vi vector<int>
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll my_rand(ll l, ll r)
{
    return uniform_int_distribution<ll>(l,r) (rng);
}


int32_t main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int tc=1;
    //cin>>tc;
    for(int tt=1; tt<=tc; tt++)
    {
        double h,r,da,dw;
        cin>>h>>r>>da>>dw;
        double a,b,c;
        double ca,cw,p;
        ca= pi*r*r*da;
        cw=pi*r*r*dw;
        p= cw-ca;

        a=p*p;
        b=2LL*ca*h*p;
        c=-p*ca*h*h;

        double det=(b*b) -(4LL*a*c);
        det = sqrt(det);
        double ans1 = (-b+det )/(2*a);
        double ans2 = (-b-det )/(2*a);

        if(ans1 >0 and ans1<=h) cout<<fixed<<setprecision(9)<<ans1<<endl;
        else cout<<fixed<<setprecision(9)<<ans2<<endl;

    }
}