B. Anany in the Army

#include <bits/stdc++.h>

using namespace std;

#define cin_2d(vec, n, m) for(int i = 0; i < n; i++) for(int j = 0; j < m && cin >> vec[i][j]; j++);
#define cout_2d(vec, n, m) for(int i = 0; i < n; i++, cout << "\n") for(int j = 0; j < m && cout << vec[i][j] << " "; j++);
#define cout_map(mp) for(auto& [f, s] : mp) cout << f << "  " << s << "\n";
#define Time cerr << "Time Taken: " << (float)clock() / CLOCKS_PER_SEC << " Secs" << "\n";
#define fixed(n) fixed << setprecision(n)
#define ceil(n, m) (((n) / (m)) + ((n) % (m) ? 1 : 0))
#define fill(vec, value) memset(vec, value, sizeof(vec));
#define Num_of_Digits(n) ((int)log10(n) + 1)
#define mod_combine(a, b, m) (((a % m) * (b % m)) % m)
#define all(vec) vec.begin(), vec.end()
#define rall(vec) vec.rbegin(), vec.rend()
#define sz(x) int(x.size())
#define debug(x) cout << #x << ": " << (x) << "\n";
#define fi first
#define se second
#define Pair pair < int, int >
#define ll long long
#define ull unsigned long long
#define Mod  1'000'000'007
#define OO 2'000'000'000
#define EPS 1e-10
#define PI acos(-1)

template < typename T = int > istream& operator >> (istream &in, vector < T > &v) {
    for (auto &x: v) in >> x;
    return in;
}

template < typename T = int > ostream& operator << (ostream &out, const vector < T > &v) {
    for (const T &x: v) out << x << ' ';
    return out;
}

void AhMeD_HoSSaM(){
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
    freopen("sticks.in", "r", stdin);
    #ifndef ONLINE_JUDGE
        freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
    #endif
}

bool can_make_triangle(vector < double > v){
    sort(all(v));
    return v[0] + v[1] > v[2];
}

double triangle_area(vector < double > v, double add){
    v[0] = add;
    if(!can_make_triangle(v)) return 0;
    double s = (v[0] + v[1] + v[2]) / 2.0;
    return sqrt(s * (s - v[0]) * (s - v[1]) * (s - v[2]));
}

double ternary_search(double k, vector < double > len){
    double l = len[0], r = min(len[0] + k, len[1] + len[2]);
    for(int i = 0; i < 100; i++){
        double g = l + (r - l) / 3.0, h = r - (r - l) / 3.0;
        (triangle_area(len, g) > triangle_area(len, h) ? r = h : l = g);
    }
    return triangle_area(len, l);
}

void Solve(){
    double k;
    vector < double > len(3);
    cin >> len >> k;
    sort(all(len));
    cout << fixed(9) << ternary_search(k, len) << '\n';
}

int main(){
    AhMeD_HoSSaM();
    int t = 1;
    cin >> t;
    while(t--)
        Solve();
    return 0;
}