#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")

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

#define el '\n'
#define F first
#define S second

typedef long long ll;
typedef long double ld;

bool multipleTestCases = 0, sublime = 0;
const int N = 4e5 + 5, INF = 1e9 + 5, mod = 1e9 + 7, LOG = 22, SQ = 500;

const ld pi = acos(-1), EPS = 1e-9;

ld h, r, da, dw;

ld calc(ld x) {
    ld mw = dw * (pi * r * r * x);
    ld ma = da * (pi * r * r * (h - x));

    return (mw * x + ma * (h - x)) / (mw + ma);
}

void doWork() {
    cin >> h >> r >> da >> dw;

    ld s = 0, e = h, m1, m2;

    for (int i = 0; i < 300; i++) {
        m1 = s + (e - s) / 3;
        m2 = e - (e - s) / 3;

        if (calc(m1) < calc(m2)) {
            e = m2;
        }
        else {
            s = m1;
        }
    }

    cout << fixed << setprecision(12) << (s + e) / 2;
}

signed main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
#endif
#ifndef ONLINE_JUDGE
    if (sublime) {
        freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
    }
#endif
    int tests = 1;
    if (multipleTestCases) {
        cin >> tests;
    }
    for (int tc = 1; tc <= tests; tc++) {
        doWork();
    }
}