#include<iostream>
#include <bits/stdc++.h>

# define ld long double
#define ll long long
#define IO ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
const int N = 4e5 + 5, mod = 998244353, M = 17;

// mass = density * volume
// m1 = ans * w
// m2 = (h - ans) * a
// CM = ( ans / 2 * ans * w   + (h + ans) / 2 * (h-ans) * a) / ()
int h, r, a, w;

ld solve(ld ans) {
    ld m1 = ans * w;
    ld m2 = (h - ans) * a;

    ld cm1 = ans / 2;
    ld cm2 = (ans + h) / 2;

    return (m1 * cm1 + m2 * cm2) / (m1 + m2);
}

void doWork() {
    cin >> h >> r >> a >> w;
    ld low = 0, high = h;
    for (int i = 0; i < 100; i++) {
        ld ans1 = low + (high - low) / 3;
        ld ans2 = high - (high - low) / 3;
        if (solve(ans1) < solve(ans2))high = ans2;
        else low = ans1;
    }
    cout << fixed << low;
}

int main() {
    IO
    int t = 1;
    //  cin >> t;
    for (int i = 1; i <= t; i++) {
        doWork();
    }
}

// n * (n+1) / 2