#include <iostream>
#include <vector>
#include <iomanip>
using namespace std;
int main(){
    int n;cin>>n;
    vector<long double> A(n);
    long double t = 0;
    for(int i = 0; n > i; i++){
        cin>>A[i];
        t = max(t,A[i]);
    }
    long long k;cin>>k;
    long double mx = t;
    long double mn = 0;
    while(mx-mn > 1e-10){
        long double ce = (mx+mn)/2;
        long long z = 0;
        for(int i = 0; n > i; i++){
            z += A[i]/ce;
            if(z >= k)break;
        }
        if(z >= k){
            mn = ce;
        }else{
            mx = ce;
        }
    }
    cout << fixed << setprecision(10) << mn << endl;
}