#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;i<n;i++)
#define REP(i,a,n) for(ll i=a;i<n;i++)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define be(v) (v).begin(),(v).end()
#define all(i,v) for(auto& i : v)
#define UQ(v) sort(be(v)), v.erase(unique(be(v)), v.end())
#define LB(x,v) (lower_bound(be(v),(x))-(v).begin())
#define UB(x,v) (upper_bound(be(v),(x))-(v).begin())
#define dout()  cout << fixed << setprecision(20)
#define randinit() srand((unsigned)time(NULL))

template<class T, class U> bool chmin(T& t, const U& u) { if (t > u){ t = u; return 1;} return 0; }
template<class T, class U> bool chmax(T& t, const U& u) { if (t < u){ t = u; return 1;} return 0; }




void solve(){
    ll n, k;
    cin >> n;
    V<ll> v(n);
    rep(i,n) cin >> v[i];
    cin >> k;
    long double L = 0.0, R = mod107;
    rep(i, 150){
    	long double mid = (L+R)/2;
    	ll a = 0;
    	rep(j, n){
    		a += v[j]/mid;
    	}
    	if(a < k) R = mid;
    	else L = mid;
    }
    dout();
    cout << L << endl;
}





int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t=1;
    // cin >> t;
    rep(i,t) solve();
}