#include <iostream>
#include <algorithm>
#include <functional>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <string>
#include <numeric>
#include <cmath>

#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;
typedef long long ll;
using P = pair<ll, ll>;

template<class T> inline bool chmin(T& a,T b) {if (a > b) {a = b; return true;} return false;}
template<class T> inline bool chmax(T& a,T b) {if (a < b) {a = b; return true;} return false;}

const ll MOD = 1000000007;
const int INF = 1<<29;
//const ll INF = (ll)1e18 + 1;

ll N, K;
vector<ll> L;
bool c(double x){
  int sum = 0;
  rep(i, N){
    sum += L[i] / x;
  }
  return sum >= K;
}

int main(){
  cin >> N;
  L = vector<ll>(N);
  rep(i, N) cin >> L[i];
  cin >> K;

  double left = 0, right = 1e10+5;
  rep(i, 10000){
    double mid = (right + left) / 2;
    if (c(mid)) left = mid;
    else right = mid;
  }
  printf("%.15f\n", left);
}