#include <bits/stdc++.h>
using namespace std;
#define rep(i, m, n) for (int i = m; i < n; ++i)
#define rem(i, m, n) for (int i = m; i >= n; --i)
typedef long long ll;

int main(){
  int N;
  cin >> N;
  vector<ll> L(N);
  rep(i, 0, N) cin >> L[i];
  ll K;
  cin >> K;
  double ok = 0;
  double ng = 1e11;
  double mid;
  rep(i, 0, 100) {
    mid = (ok + ng) / 2;
    ll cnt = 0;
    rep(j, 0, N) cnt += L[j] / mid;
    if(cnt >= K) ok = mid;
    else ng = mid;
  }
  printf("%.12lf\n", mid);
  return 0;
}