#include <cstdio>
#include <iostream>
#include <algorithm>
#include <complex>
#include <queue>
#include <map>
using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define pb push_back
#define ALL(a) (a).begin(),(a).end()

#define EPS (1e-10)
#define EQ(a,b) (abs((a)-(b)) < EPS)

#define PI 3.1415926535

typedef long long ll;
//typedef pair<int, int> P;
//typedef complex<double> C;

const int MAX_N = 200000;

int N;
double L[MAX_N];
ll K;

void input() {
    cin >> N;
    REP(i, N) cin >> L[i];
    cin >> K;
}

ll count(double length) {
    ll cnt = 0;
    REP(i, N) {
        cnt += (ll) (L[i] / length);
    }
    return cnt;
}

void solve() {
    double ok = 1e-10;
    double ng = 1e9 + 1;
    REP(i, 100) {
        double mid = (ok + ng) / 2;
        if (count(mid) >= K) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    printf("%.14f\n", ok);
}

int main() {
    input();
    solve();
    return 0;
}