#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef ll li;
typedef pair<ll,ll> PI;
#define rep(i,n) for(int i=0;i<(int)(n);++i)
#define REP(i, n) rep (i, n)
#define F first
#define S second
#define mp(a,b) make_pair(a,b)
#define pb(a) push_back(a)
#define SZ(a) (int)((a).size())
#define ALL(a) (a).begin(),(a).end()
#define FLL(a,b) memset((a),b,sizeof(a))
#define CLR(a) memset((a),0,sizeof(a))
#define FOR(it,a) for(__typeof(a.begin())it=a.begin();it!=a.end();++it)
#define FORR(it,a) for(__typeof(a.rbegin())it=a.rbegin();it!=a.rend();++it)
template<typename T,typename U> ostream& operator<< (ostream& out, const pair<T,U>& val){return out << "(" << val.F << ", " << val.S << ")";}
template<class T> ostream& operator<< (ostream& out, const vector<T>& val){out << "{";rep(i,SZ(val)) out << (i?", ":"") << val[i];return out << "}";}
#define declare(a,it) __typeof(a) it=a
const double EPS = 1e-8;

const int dx[]={1,0,-1,0,1,1,-1,-1,0};
const int dy[]={0,1,0,-1,-1,1,-1,1,0};

int main(int argc, char *argv[])
{
  int n;
  cin >> n;
  double low = 0;
  double up = 1e20;
  vector<int> l(n);
  rep(i,n) cin >> l[i];
  ll k;
  cin >> k;
  rep(i,1000){
    double mid = (low+up)/2;
    ll nu = 0;
    rep(j,n) nu += l[j]/mid;
    if(nu>=k) low = mid;
    else up = mid;
  }
  printf("%.18f\n",low);
}