#include<bits/stdc++.h>
using namespace std;

typedef long long int ll;
typedef unsigned long long int llu;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pair<int, int> > vii;

#define rrep(i, m, n) for(int i=m; i<n;  i++)
#define erep(i, n)    for(int i=1; i<=n; i++)
#define  rep(i, n)    for(int i=0; i<n;  i++)
#define rrev(i, m, n) for(int i=n-1; i>=m; i--)
#define erev(i, n)    for(int i=n; i>=1; i--)
#define  rev(i, n)    for(int i=n-1; i>=0; i--)
#define EACH(v)       (v).begin(), (v).end()
#define CNT(a, n, x)  (upper_bound(a, a+n, x)-lower_bound(a, a+n, x))
#define minup(m, x)   (m=min(m, x))
#define maxup(m, x)   (m=max(m, x))
#define mp            make_pair

#define INF 1000000000
#define MOD 1000000009
#define EPS 1E-15

#define MAX_N 200000

ll n;
ll l[MAX_N];
ll k;
double mid, mid2;

int main()
{
  cin >> n;
  rep(i, n) cin >> l[i];
  cin >> k;

  double left = 0;
  double right = INF;
  mid = (left + right) / 2.0;
  while(abs(mid-mid2) >= EPS){
    ll num = 0;
    rep(i, n) num += (ll)(l[i] / mid);
    if(num >= k) left = mid;
    else right = mid;
    mid2 = mid;
    mid = (left + right) / 2.0;
  }

  printf("%.15f\n", mid);

  return 0;
}