#include <bits/stdc++.h>

#define mp       make_pair
#define mt	 make_tuple
#define pb       push_back
#define rep(i,n) for(int i=0;i<(n);i++)

using namespace std;

typedef    long long          ll;
typedef    unsigned long long ull;
typedef    pair<int,int>      pii;
typedef    pair<long,long>    pll;

const int INF=1<<29;
const double EPS=1e-9;
const int MOD = 100000007;

const int dx[]={1,0,-1,0},dy[]={0,-1,0,1};
int N,K;
vector<ll> L;
bool check(double med){
  ll res = 0;
  for (int i = 0; i < N; i++){
    res += L[i] / med;
  }
  return res >= K ? true : false;
}
int main(){
  cin >> N;
  L.resize(N);
  for (int i = 0; i < N; i++){
    cin >> L[i];
  }
  sort(L.begin(),L.end());
  cin >> K;
  double left,right;
  left = 0;
  right = 1e10;
  for (int i = 0; i < 300; i++){
    double med = (right + left) / 2.0;
    if (check(med)){
      left = med;
    }else{
      right = med;
    }
  }
  printf("%.20lf\n", left);
}