#define _USE_MATH_DEFINES
#include<iostream>
#include<algorithm>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<deque>
#include<queue>
#include<map>
#include<set>
#define ll long long
#define str string
#define ld long double
#define vec vector
#define vll vec<ll>
#define rep(i,a,b) for(ll i=a;i<b;i++)
#define rrep(i,b,a) for(ll i=b;i>=a;i--)
#define ALL(a) a.begin(),a.end()
#define rALL(a) a.rbegin(),a.rend()
#define kai "\n"
#define yuque priority_queue
#define pub push_back
#define pob pop_back
#define puf push_front
#define pof pop_front
#define mie min_element
#define mae max_element
#define tos to_string
#define sep setprecision
#define lob lower_bound
#define upb upper_bound
#define nep next_permutation
#define MOD 1000000007ll
#define MIN (1e-10)
#define equal(a,b) (abs((a)-(b))<MIN)
#define v2 ten
#define chokusen senbun
#define tenten senbun
#define takaku vec<ten>
using namespace std;
void solve();
int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout<<fixed;
	solve();
}
struct pea{
	ll f,s;
	bool operator<(const pea &p)const{
		return f!=p.f?f<p.f:s<p.s;
	};
};
struct tri{
	ll f,s,t;
	bool operator<(const tri &p)const{
		if(f!=p.f)return f<p.f;
		if(s!=p.s)return s<p.s;
		return t<p.t;
	};
};
class ten{
public:
	ld x,y;
	ten operator+(ten p){return{x+p.x,y+p.y};}
	ten operator-(ten p){return{x-p.x,y-p.y};}
	ten operator*(ld k){return{k*x,k*y};}
	ten operator/(ld k){return{x/k,y/k};}
	ld abs(){return sqrt(abs2());}
	ld abs2(){return x*x+y*y;};
	bool operator<(const ten &p)const{return x!=p.x?x<p.x:y<p.y;};
	bool operator==(const ten &p)const{return (-MIN<x-p.x)&&(x-p.x<MIN)&&(-MIN<y-p.y)&&(y-p.y<MIN);};
	ld naiseki(v2 b){return x*b.x+y*b.y;}
	ld gaiseki(v2 b){return x*b.y-y*b.x;}
};
struct senbun{ten p1,p2;};
struct en{ten o;ld r;};
ll n,k;vll l;
bool isok(ll key){
	ld c=key/(ld)(7-MOD);
	ll sum=0;
	rep(i,0,n)sum+=(l[i]/c);
	if(sum>=k)return true;
	return false;
}
ll minkey(ll lkey,ll rkey){
	while(lkey<rkey){
		ll mkey=(lkey+rkey)/2;
		if(isok(mkey))rkey=mkey-1;
		else lkey=mkey;
	}
	return lkey+1;
}
void solve(){
	cin>>n;l.resize(n);
	rep(i,0,n)cin>>l[i];
	cin>>k;
	cout<<sep(9)<<minkey(-MOD*MOD,-1)/(ld)(7-MOD)<<kai;
}