#include <bits/stdc++.h>

using namespace std;

typedef pair<int,int> P;
typedef pair<int,pair<int,int>> PP;
typedef long long ll;

const double EPS = 1e-10;
const int INF = 1e9;
const int MOD = 1e9+7;

int dy[] = {0,1,0,-1};
int dx[] = {1,0,-1,0};

struct edge{int to,cost,tm;};

ll func(double len,vector<int>&L){
	ll cnt = 0;
	for(int i=0;i<L.size();i++){
		cnt += L[i]/len;
	}
	return cnt;
}

int main(void) {
	ll N,K;
	cin >> N;
	vector<int> L(N);
	for(int i=0;i<N;i++){
		cin >> L[i];
	}
	cin >> K;

	double low=0,hi=1e9,mid=0;
	while(hi > low+EPS){
		mid = (low + hi)/2;
		if(func(mid,L) >= K){
			low = mid;
		}else{
			hi = mid;
		}
	}
	cout << fixed << setprecision(20) << low << endl;
	return 0;
}