#include <iostream>
#include <algorithm>
#include <cstdio>

using namespace std;

int N, K;
int L[200010];

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

    cin >> K;

    double right = 1e9;
    double left = 0;
    double mid = 0;

    for(int i = 0; i < 100; i++)
    {
        mid = (right + left) / 2;
        long long tmp = 0;
        for(int i = 0; i < N; i++)
        {
            tmp += L[i] / mid;
        }
        if(tmp >= K) left = mid;
        else right = mid;
    }

    printf("%.14f", left);

    return 0;
}