#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;

#define fi first
#define se second
#define pp push_back
#define all(x) (x).begin(), (x).end()
#define Ones(n) __builtin_popcount(n)
#define endl '\n'
#define mem(arrr, xx) memset(arrr,xx,sizeof arrr)
#define PI acos(-1)
//#define int long long
#define debug(x) cout << (#x) << " = " << x << endl

void Gamal() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
#ifdef Clion
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}

int dx[] = {+0, +0, -1, +1, +1, +1, -1, -1};
int dy[] = {-1, +1, +0, +0, +1, -1, +1, -1};

const double EPS = 1e-9;
const ll OO = 0X3F3F3F3F3F3F3F3F;
const int N = 2e5 + 5, INF = INT_MAX, MOD = 1e9 + 7, LOG = 20;

int h,ri,da,dw;
ld get(ld m){
    ld water = PI * ri * ri * m * dw;
    ld air = PI * ri * ri * (h - m) * da;
    return (water * h/2 + air * (m + (h - m)/2))/(water + air);
}

void solve() {
    cin >> h >> ri >> da >> dw;
    ld l = 0,r = h;
    for (int i = 0; i < 100; ++i) {
        ld m1 = l + (r - l)/3;
        ld m2 = r - (r - l)/3;
        ld c1 = get(m1);
        ld c2 = get(m2);
        if(c1 <= c2) l = m1;
        else r = m2;
    }
    cout << fixed << setprecision(7) << l << endl;
}


signed main() {
    Gamal();
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}