#include <bits/stdc++.h>
using namespace std;
const int NUM=10010;
const double PI=acos(-1);
double a[NUM+10];
int n,f;
bool check(double x)
{
	int d=0;
	for (int i=0;i<f;i++)
		d+=floor(a[i]/x);
	if (d>=n+1) return 1;
	return 0;
}
int main()
{
	int R;
	double l=0,r=0,ans;
	scanf("%d%d",&f,&n);
	for (int i=0;i<f;i++)
	{
		scanf("%d",&R);
		a[i]=R*R*PI;
		r=max(r,a[i]);
	}
	//sort(a,a+n);
	while ((r-l)>0.00001)
	{
		double mid=(r+l)/2.0;
		if (check(mid))
		{
			ans=mid;
			l=mid;
		}
		else
			r=mid;
	}
	printf("%.3f",ans);
	return 0;
}