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

using namespace std;

typedef long long ll;

#define MOD 1000000007

int main() {
  int n;
  cin >> n;
  vector<ll> l(n);
  for (int i = 0; i < n; ++i) {
    cin >> l[i];
  }
  ll k;
  cin >> k;
  double ok = 0, ng = 1e9 + 1;
  for (int i = 0; i < 100; ++i) {
    double mid = (ok + ng) / 2.0;
    ll cnt = 0;
    for (int i = 0; i < n; ++i) {
      cnt += (l[i] / mid);
    }
    if (k <= cnt) {
      ok = mid;
    } else {
      ng = mid;
    }
  }
  printf("%.15f\n", ok);
  return 0;
}