#include <algorithm>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <iostream>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
 
using namespace std;
 
#define sz size()
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(c) (c).begin(), (c).end()
#define rep(i,a,b) for(int i=(a);i<(b);++i)
#define clr(a, b) memset((a), (b) ,sizeof(a))
 
#define MOD 1000000009

long long n;
vector<int> v;
long long k;

int check(double d){
  long long a = 0;
  rep(i,0,n){
    a += 1.*v[i]/d;
  }
  if(k <= a)return 1;
  return 0;
}

int main(){
  cin >> n;
  rep(i,0,n){
    long long a;
    cin >> a;
    v.pb(a);
  }
  cin >> k;
  double low = 0.0;
  double high = 10000000005.0;

  while(high - low > 1e-12){
    double mid = (low + high) / 2;
    if(check(mid)){
  	  low = mid;
    }
    else{
      high = mid;
    }
  }
  cout << low << endl;
  return 0;
}