#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const ld eps = 1e-10;
const ld pi = acos(-1);

int n;
ld l[200010];
ll k;

ld solve() {
    ld lb = 0.0, ub = 1e10;
    for (int t = 0; t < 200; t++) {
        ld mid = (lb + ub) / 2;
        ll m = 0;
        for (int i = 0; i < n; i++) {
            m += (ll)(l[i]/mid + eps);
        }
        if (m >= k) {
            lb = mid;
        } else {
            ub = mid;
        }
    }
    
    return lb;
}

void input() {
    cin >> n;
    for (int i = 0; i < n; i++)
        cin >> l[i];
    cin >> k;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}