#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000

int main(){
	
	int N;
	cin>>N;
	
	vector<long long> L(N);
	rep(i,N)cin>>L[i];
	
	long long K;
	cin>>K;
	
	double ok = 0.0,ng = 1e10;
	rep(_,100){
		double mid = (ok+ng)/2;
		long long sum = 0LL;
		rep(i,N){
			sum += L[i] / mid;
		}
		if(sum >= K)ok = mid;
		else ng = mid;
	}
	cout<<fixed<<setprecision(10)<<ok<<endl;
	
	return 0;
}