#include <algorithm>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <vector>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rrep(i, n) for (int i = (n)-1; i >= 0; i--)
using namespace std;
typedef long long int lli;
lli MOD = 1000000007;
lli k, n;
double l[200005];
bool ok(double len)
{
    lli sum = 0;
    rep(i, n) sum += (lli)(l[i] / len);
    return k <= sum;
}
int main()
{
    cin >> n;
    double up = 1e13;
    double low = 0;
    rep(i, n) cin >> l[i];
    cin >> k;
    rep(i, 100)
    {
        double mid = (low + up) / 2;
        if (!ok(mid)) {
            up = mid;
        } else {
            low = mid;
        }
    }
    printf("%.15f\n", up);
}