#include<bits/stdc++.h>
using namespace std;

using ll=long long;
using P=pair<int,int>;

#define int long long 

const int MOD=1e9+7;
const int INF=1<<30;
const int MAX=1e5;

template<class T>
inline void xmin(T &a, T b){a=(a<b)?a:b;}
template<class T>
inline void xmax(T &a, T b){a=(a>b)?a:b;}

int n;
double l[200000];
double k;

bool isOK(double mid, double key){
    int sum=0;
    for(int i=0; i<n; i++){
        sum+=l[i]/mid;
    }
    if(sum>=key)return true;
    else return false;
}

double binary_search(double key){
    double ng=10000000000;
    double ok=0;
    for(int i=0; i<100; i++){
        double mid=(ng+ok)/2;
        if(isOK(mid, key)) ok=mid;
        else ng=mid;
    }
    return ok;
}

void solve(){
    cin>>n;
    for(int i=0; i<n; i++){
        cin>>l[i];
    }
    cin>>k;
    printf("%.12f", binary_search(k));
}

signed main(){
    //while(1)
    solve();
}