#include<bits/stdc++.h>
#define int long long
using namespace std;
int t, n, m, r, k, a[100005], h[100005], l[100005];
long double ans;
long long cnt;
bool cmp(int p, int q) {
	return p > q;
}
struct node {
	int name, num;
	bool operator <(const node p)const {
		return num < p.num;
	}
};
priority_queue<node> q;
signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin >> t;
	while (t--) {
		cin >> n >> m >> r >> k;
		for (int i = 1; i <= n; i++) {
			h[i] = min(n - r + 1, i) - (max(1ll, i - r + 1)) + 1;
		}
		for (int i = 1; i <= m; i++) {
			l[i] = min(m - r + 1, i) - max(1ll, i - r + 1) + 1;
		}
		cnt = 0;
		for (int i = 1; i <= n; i++) a[i] = 0;
		sort(h + 1, h + n + 1, cmp);
		sort(l + 1, l + m + 1, cmp);
		while (q.size()) q.pop();
		for (int i = 1; i <= n; i++) {
			a[i] = 1;
			q.push(node{i, h[i]*l[1]});
		}
		node u;
		for (int i = 1; i <= k; i++) {
			u = q.top();
			cnt += u.num;
			a[u.name]++;
			if (a[u.name] <= m) {
				q.push(node{u.name, h[u.name]*l[a[u.name]]});
			}
			q.pop();
		}
		ans = cnt * 1.0 / ((n - r + 1) * (m - r + 1));
		cout << fixed << setprecision(10) << ans << "\n";
	}
}