#include <bits/stdc++.h>
using namespace std; typedef long double ld; typedef long long ll;
typedef unsigned long long ull;
#define MP make_pair
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define FORR(x,arr) for(auto& x:arr)
#define VI vector<int>
#define PII pair<int, int>
#define FI first 
#define SE second
#define ALL(x) (x).begin(), (x).end()
const int INF=1<<30; const ll LINF=1LL<<60 ; const ll MOD=1e9+7 ;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
//-------------------
const int MX = 200000 + 7;
const ld LMX = 1e10+10;
ld l[MX];
int n;
ll k;

ll num(ld leng){
	ll ans = 0;
	FOR(i,1,n){
		ans += l[i]/leng;
	}
	return ans;
}

ld lt = 0, rt = LMX, mid;

void solve(){	
	FOR(i,1,1000){
		mid = (lt+rt)/2;
		if(num(mid) < k) rt = mid;
		else lt = mid;
	}
}

int main(){
	cin >> n;
	FOR(i,1,n){
		cin >> l[i];
	}
	cin >> k;
	solve();	
	cout << fixed << setprecision(10) << mid;
    return 0;
}