#include <bits/stdc++.h>
using namespace std;

#define lp(i, a, b) for (int i = (int)(a); i < (int)(b); i++)
#define rep(i, n) lp(i, 0, n)
#define rlp(i, a, b) for (int i = (int)(b) - 1; i >= (int)(a); i--)
#define rrep(i, n) rlp(i, 0, n)

#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define all(c) begin(c), end(c)

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> pr;
typedef tuple<int, int, int> tp;

template<typename T>
inline bool chmin(T &a, T b){
	if (a <= b) return false;
	a = b; return true;
}

template<typename T>
inline bool chmax(T &a, T b){
	if (a >= b) return false;
	a = b; return true;
}

template<typename T>
inline void unique(T &c){
	sort(all(c));
	c.erase(unique(all(c)), end(c));
}

template<typename T>
inline T sq(T a){
	return a * a;
}

template<typename T>
inline size_t index_of(vector<T> &c, T x){
	return lower_bound(all(c), x) - begin(c);
}

int n;
double l[200010];
long long k;

bool ok(double x)
{
	long long cnt = 0;
	rep(i, n) cnt += (long long)(l[i] / x);
	return cnt >= k;
}

int main()
{
	cin >> n;
	rep(i, n) cin >> l[i];
	cin >> k;
	double lb = 0.0, ub = 1e15;
	rep(i, 200){
		double md = (lb + ub) / 2;
		(ok(md) ? lb : ub) = md;
	}
	printf("%.20f\n", lb);
}