#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <math.h>
#include <string.h>
#include <map>
#include <numeric>
#include <random>
#include <queue>
#include <deque>
#include <tuple>
#include <iomanip>
#include <iterator>
#include <functional>

using namespace std;
typedef long long ll;

const int INF = (1 << 30) - 1;
const ll INFLL= (1LL << 61) - 1;
const int MOD = 1000000007;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)

int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int N;
  cin>>N;
  vector<long double> L(N);
  REP(i,N)cin>>L[i];
  ll K;
  cin>>K;
  long double high=10000000000000000,low=0;
  long double mid;

  REP(loop,200){
    ll cnt=0;
    mid=(high+low)/2.0;
    REP(i,N){
      cnt+=ll(L[i]/mid);
    }
    if(cnt>=K){
      low=mid;
    }else{
      high=mid;
    }
  }
  cout<<setprecision(15)<<mid<<endl;
}