#include <bits/stdc++.h> 
using namespace std;
const int N = 210000;
const double eps = 1e-6; 
int n, m;
double a[N];

bool check(double x) {
    int sum = 0;
    for (int i = 1; i <= n; i++) {
        sum += int(a[i] / x);
    }
    return sum >= m + 1;
}

int main() {
    scanf("%d%d", &n, &m);
    double l = 0, r = 0, ans;
    for (int i = 1; i <= n; i++) {
        scanf("%lf", &a[i]);
        a[i] = a[i] * a[i] * 3.141592653589;
        r = max(r, a[i]);
    }
    while (l <= r) {
        double mid = (l + r) / 2;
        if (check(mid)) {
            l = mid + eps;
            ans = mid;
        } else {
            r = mid - eps;
        }
    }
    printf("%.3lf\n", ans);
    return 0;
}

#include<bits/stdc++.h> 
using namespace std;
const int N=210000;
const double eps=1e-6; 
int n,m;double a[N];
bool check(double x)
{
    int sum=0;for(int i=1;i<=n;i++)sum+=int(a[i]/x);
    if(sum>=m+1)return 1;else return 0;
}
int main()
{
    scanf("%d%d",&n,&m);
    double l=0,r=0,ans;
    for(int i=1;i<=n;i++)
    {
        scanf("%lf",&a[i]); a[i]=a[i]*a[i]*3.141592653589;
        r=max(r,a[i]);
    }
    while(l<=r)
    {
        double mid=(l+r)/2;
        if(check(mid)) l=mid+eps,ans=mid;
        else           r=mid-eps;
    }
    printf("%.3lf\n",ans);
    return 0;
}