#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <array>
#include <map>
#include <stack>
#include <queue>
#include <set>

using namespace std;

long ls[200000];

long f(double x, int N) {
    long count = 0;
    for (int i = 0; i < N; ++i) {
        count += (long) (ls[i] / x);
    }
    return count;
}


int main() {

    int N;
    cin >> N;


    long L;
    for (int i = 0; i < N; ++i) {
        cin >> L;
        ls[i] = L;
    }

    long K;
    cin >> K;

    double a = 0;
    double b = 1000000000;

    double x;
    for (int j = 0; j < 100; ++j) {

        x = (a + b) / 2;

        if (f(x, N) >= K) {
            a = x;
        } else {
            b = x;
        }
    }

    printf("%.14f\n", x);

    return 0;
}