#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <stack>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;

ll N, K;
vector<ll> v;

bool C(double x){
  ll cnt = 0;
  rep(i,v.size()){
    double num = floor(v[i]/x);
    cnt += (ll)(num+0.5);
  }
  return K <= cnt;
}


int main(){
  cin >> N;
  rep(i,N){
    ll a;
    cin >> a;
    v.push_back(a);
  }
  cin >> K;
  
  double lb=0, ub=10e10;
  rep(i,100){
    double mid = (lb+ub)/2.0;
    if(C(mid)) lb = mid;
    else ub = mid;
  }
  printf("%.15lf\n", ub);
  return 0;
}