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

#define REP(i, n) for(int i=0; i<(n); i++)
#define int long long
#define ALL(a) (a).begin(),(a).end()
#define SUM(a) accumulate(ALL(a), 0)
#define FOR(i, a, b) for(int i=(a);i<(b);i++)

int N, K;
vector<int> L(222222);
signed main()
{
    cin >> N;
    REP(i,N) cin >> L[i];
    cin >> K;
    sort(ALL(L));
    reverse(ALL(L));
    double maxl = 1.0 * SUM(L) / K;
    if (K <= N) {
        cout << L[K-1] << endl;
        return 0;
    }

    int cut = (int)(L[0] / maxl);
    while(true) {
        double maxlen = min(1.0 *  L[0] / cut, (double)L[N-1]);
        int cnt = N + cut - 1;
        bool ok = false;
        FOR(i,1,N) {
            if (cnt >= K) {
                ok = true;
                break;
            }
            int cuti = (int)(L[i] / maxlen);
            maxlen = min(maxlen, 1.0 * L[i] / cuti);
            cnt += cut - 1;
        }
        if (ok) {
            printf("%.14f\n", maxlen);
            return 0;
        }
        cut++;
    }
}