#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <map>
#include <math.h>
#include <cstring>

using namespace std;

#define REP(i,n)	for(int i=0;i<(n);++i)
#define REPS(i,s,t)	for(int i=(s);i<(t);++i)

#define INF 		2000000007
#define MOD			998244353

#define MAX 		100005

typedef unsigned int 			uint;
typedef unsigned long long int	ull;
typedef long long int ll;


bool check(double n,ll K,vector<uint> a){
	for(auto t : a)
		K -= floor(t/n);
	return (K<=0);
}

int main(void) {
	int N;cin>>N;
	vector<uint> L(N);
	REP(i,N)cin>>L[i];
	ll K;cin>>K;

	double l=1e-8,r=1e8;
	double middle = (l+r)/2;
	REP(i,1000){
		if(check(middle,K,L)){
			l = middle;
			middle = (l+r)/2;
		}
		else{
			r = middle;
			middle = (l+r)/2;
		}
	}
	printf("%0.7lf\n",middle);

    return 0;
}