#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

int main(){
    int N; cin >> N;
    int L[200000];
    REP(i,N) cin >> L[i];
    ll K; cin >> K;

    double l = 0, r = 1e9;
    REP(j,100){
        double c = (l+r)/2;
        ll v = 0;
        REP(i,N) v+=(ll)(L[i]/c);
        if(v >= K) l = c; else r = c;
    }
    double res = (l+r)/2;
    cout << fixed << setprecision(15) << res << endl;
    return 0;
}