#include<iostream>
#include<algorithm>
#include<vector>
#include<cstdio>
using namespace std;
typedef long long ll;
ll K;
vector<ll> L;
bool split(double num){
    ll eda=0;
    for(int i=0;i<L.size();i++){
        eda+=L[i]/num;
    }
    if(eda>=K)  return true;
    return false;
}
int main(){
    double lb=0,ub=0,mid;
    ll N,x;
    cin >> N;
    while(N--){
        cin >> x;
        L.push_back(x);
        if(ub<x)    ub = x;
    }
    cin >> K;
    do{
        mid=(lb+ub)/2;
        if(split(mid))    lb=mid;
        else    ub=mid;
    }while(ub-lb>0.0000000001);
    printf("%.10lf\n",lb);
    return 0;
}