#include <bits/stdc++.h>

using namespace std;

#define int long long
#define vint vector<int>
#define pb push_back
#define ALL(v) (v).begin(), (v).end()
#define INF LLONG_MAX


void solve(){
    int n; cin >> n;
    double sum = 0;
    vector<double> l(n);
    for(int i = 0; i < n; i++){
    	cin >> l[i];
    	sum += l[i];
    }
    int k; cin >> k;
    double ans = 0.0;
    double le = 0, r = sum / k;
    while(r - le > 1e-9){
    	double mid = (le + r) / 2.0;
    	int cnt = 0;
    	for(int i = 0; i < n; i++){
    		cnt += (int)(l[i] / mid);
    	}
    	if(cnt >= k){
    		le = mid;
    		ans = mid;
    	}
    	else r = mid;
    }
    cout << fixed << setprecision(10) << ans;
}

signed main(){

    ios_base::sync_with_stdio(0); cin.tie(0);

    solve();

}