LA3635.cpp

#include <bits/stdc++.h>

#define EPS 1e-6
#define MOD 1000000007
#define inf 0x3f3f3f3f
#define llinf 0x3f3f3f3f3f3f3f3f

#define fi first
#define se second
#define sz size()
#define pb push_back
#define ende '\n'

#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define mset(x, y) memset(&x, (y), sizeof(x))

using namespace std; 

typedef long long ll;
typedef pair<int,int> ii;

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout << setprecision(9) << fixed;

  int t; cin >> t;
  while (t--) {
    int n, f; cin >> n >> f;
    vector<double> v(n); 
    for (auto &i : v)
      cin >> i;

    double l = 0.0, r = (double) llinf;
    for (int i = 0; i < 300; ++i) {
      double m = (l + r) / 2.0;   
      int p = 0;

      for (int j = 0; j < n; ++j)
        p += (int) floor((v[j] * v[j] * M_PI) / m);

      if (p >= f + 1)
        l = m;
      else
        r = m;
    }

    cout << l << ende;
  }

  return 0;
}