#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);
int count(double n) {
    int cnt = 0;
    REP(j,N) {
        cnt += (int)(L[j] / n);
    }
    return cnt;
}
signed main()
{
    cin >> N;
    REP(i,N) cin >> L[i];
    cin >> K;
    if (K <= N) {
        cout << L[K-1] << endl;
        return 0;
    }

    double high = 1e9;
    double low = 0.0;
    REP(i,100) {
        double l = (high + low) / 2.0;
        int cnt = count(l);
        if (cnt >= K) {
            low = l;
        } else {
            high = l;
        }
    }
    printf("%.15f\n", low);
}