#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>

#define el '\n'
#define FIO ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;
typedef long double ld;
typedef complex<ld> pt;
typedef unsigned long long ull;

template<typename T, typename X>
using hashTable = gp_hash_table<T, X>;
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<typename T>
using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;

// mt19937_64 for long long
mt19937 rng(std::chrono::system_clock::now().time_since_epoch().count());

int h, da, dw;

ld calc(ld wh)
{
    ld c1 = wh / 2;
    ld c2 = wh + (h - wh) / 2;
    ld dist = c2 - c1;
    ld m1 = wh * dw;
    ld m2 = (h - wh) * da;
    return (c1 * m1 + c2 * m2) / (m1 + m2);
}

void doWork()
{
    int rd;
    cin >> h >> rd >> da >> dw;
    ld l = 1e-8, r = h;
    for(int _ = 0; _ < 1000; ++_)
    {
        ld m1 = l + (r - l) / 3;
        ld m2 = r - (r - l) / 3;
        if(calc(m1) < calc(m2))
            r = m2;
        else l = m1;
    }
    cout << fixed << setprecision(12) << calc(l) << '\n';

}

signed main()
{
    FIO
    int T = 1;
//    cin >> T;
    for(int i = 1; i <= T; i++)
        doWork();
}