#include<bits/stdc++.h>

using namespace std;

vector <int> pies;

double binarysearch( double l, double r, int f){
    int soma=0;
    double mid=(l+r)/2;
    for(int i=0; i<pies.size(); i++){
        soma+=pies[i]/mid;
    }
    if(abs(r-l)<0.00001) return mid;
    if(soma >= f+1) return binarysearch(mid, r, f);
    return binarysearch(l,mid,f);
}

int main(){

    int t, n,f,aux;
    cin>>t;

    for(int i=0;i<t;i++){
        int ma=0;
        cin>>n>>f;
        for(int j=0;j<n;j++){
            cin>>aux;
            pies.push_back(aux*aux);
            ma=max(ma,aux*aux);
        }
        printf("%.4f\n", binarysearch(0,ma,f)*M_PI);
        pies.clear();
    }

    return 0;
}