#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
using namespace std;
typedef long long ll;
double INF = 1e9;
double EPS = 1e-9;
int MOD = 1e9+7;
vector<ll> V;
ll countup(double len){
    ll cnt = 0;
    for(auto i:V){
        cnt += (ll)floor(i / len);
    }
    return cnt;
}
main(){
   ll N,K;
   cin >> N;
   V.resize(N);
   rep(i,N)scanf("%lld",&V[i]);
   cin >> K;
   double ok = EPS,ng = INF;
   //while(fabs(ok - ng) > EPS){
    for(int i = 0;i < 100;i++){
       double mid = (ok + ng) / 2;
       if(countup(mid) >= K)ok = mid;
       else                 ng = mid;
       //cout << ok << endl;
   }
   printf("%.9lf\n",ok);
}