#include<bits/stdc++.h>
using namespace std;
long long n,m;
vector<long double> a;
bool check(long double x){
    long long cnt=0;
    for(int i=0;i<n;i++){
        cnt+=floor(a[i]/x);
    }
    return cnt>=m;
}
void lookfor(long double small,long double big){
    for(int i=0;i<100;i++){
        long double mid=(small+big)/2;
        if(check(mid)) small=mid;
        else big=mid;
    }
    cout<<fixed<<setprecision(15)<<small;
}
int main(){
    cin>>n;
    a.resize(n);
    long double total=0;
    long double mx=0;
    for(int i=0;i<n;i++){
        cin>>a[i];
        total+=a[i];
        mx=max(mx,a[i]);
    }
    cin>>m;
    lookfor(0,total/m);
}