#include<iostream>
using namespace std;
typedef long long ll;
int main(){
  ll n,k;
  ll sum;
  double s=0,e=10000000000,ans,si;
  cin >> n;
  double l[n];
  for(int i=0;i<n;i++){
    cin >> l[i];
  }
  cin >> k;
  for(int i=0;i<100;i++){
    si = (e+s)/2.0;
    sum=0;
    for(int j=0;j<n;j++){
      sum += (l[j])/si;
      if(sum>=k) break;
    }
    if(sum>=k){
      s = si;
    }else{
      e = si;
    }
  }
  ans = (e+s)/2;
  printf("%.15lf\n",ans);
}