#include <iostream>
using namespace std;
double s[10000];
int main()
{
//	freopen("C:\\ACMData.txt","r",stdin);
	int t,N,F,p,tmp;  
	scanf("%d",&t);
	while(t)
	{
        scanf("%d%d",&N,&F); F++;
        p=0;
		while(p<N){
			scanf("%d",&tmp);  s[p] = (double)tmp*(double)tmp;
			p++;
		}
        double max = 100000000.0; double min =0.0;
		while(max-min > 0.000001){
			double mid =(max+min)/2.0;
			p=0;  int num=0;
			while(p<N){
				if( s[p] >= mid)
                     num +=(int) (s[p] / mid);
			   p++;
			   if( num > F)
				   break;
			}
			if( num>=F)
				min = mid;
			else
				max = mid;
		}
		double rst = (max+min)/2.0;
		printf("%.5lf\n",rst*3.14159265);
		t--;
	}
	return 1;
}

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