#include <iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<iomanip>
#include<map>
#include<queue>
#include<set>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(ll i = n-1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
#define RALL(a) rbegin(a),rend(a)
typedef long long ll;
typedef long double ld;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
const ll INF = 1e18;
ll mod = 1e9 + 7;
int n;ll k;
bool ch(ld L, vector<ld> a) {
    ll cnt = 0;
    rep(i, n) {
        cnt += (ll)(a[i] / L);
    }if (cnt >= k)return 1;
    else return 0;
}
int main() {
    cin >> n; vector<ld> l(n);
    rep(i, n) cin >> l[i];
    cin >> k;
    ld ok = 0, ng = 1e9;
    rep(i,100) {
        ld mid = (ng + ok) / 2;
        if (ch(mid, l)) ok = mid;
        else ng = mid;
    }cout << fixed << setprecision(10) << ok << endl;
}