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

int h, r, da, dw;
const double PI = acos(-1);

double calc(double wh){
    double water_center = wh * 0.5;
    double air_center = (h - wh) * 0.5 + wh;
    double d = (air_center - water_center);

    double v_water = wh * PI * r * r;
    double v_air = (h - wh) * PI * r * r;

    double weight_water = dw * v_water;
    double weight_air = da * v_air;

    double take = d * (1.0 * weight_air / (weight_air + weight_water));
    return water_center + take;
}


int main() {
    cin.tie(0);cin.sync_with_stdio(0);
    cout.tie(0);cout.sync_with_stdio(0);

    cin>>h>>r>>da>>dw;
    double eps = 1e-10;
    double L= 0, R= h, ans;
    while(R - L > eps)
    {
        double m1= L + (R - L) / 3;
        double m2= R - (R - L) / 3;
        double f1 = -calc(m1);
        double f2 = -calc(m2);
        if(f1 < f2)
            L= m1;
        else
            R= m2, ans= R;
    }

    cout<<fixed<<setprecision(10)<<ans<<"\n";
}