#include <bits/stdc++.h>

using namespace std;
#define endl "\n"
typedef long long ll;
#define int long long
int n, k;
int a[200005];
bool check(double x) {
  int ans = 0;
  for (int i = 1; i <= n; i++) ans += (int)a[i] / x;
  return ans >= k;
}
void solved() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  cin >> k;
  double l = 0, r = 1e9;
  for (int i = 1; i <= 1000; i++) {
    double mid = (l + r + 1) / 2;
    if (check(mid))
      l = mid;
    else
      r = mid - 1;
  }
  printf("%.15lf\n", l);
}
signed main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  /*int t = 1;
  cin >> t;
  while (t--)*/
  solved();

  return 0;
}