#include<iostream>
#include<cstdio>
using namespace std;
long long N,K;
double m,M,mid,L[200000];
int check(double mid){
    int count=0;
    for(int i=0;i<N;i++) count += (int)(L[i]/mid);
    if(count>=K)    return 1;
    else return 0;
}
int main(){
    cin >> N;
    for(int i=0;i<N;i++)    cin >> L[i];
    cin >> K;
    m = 0;
    M=10000000000;
    for(int i=0;i<100;i++){
        mid = (m+M)/2;
        if(check(mid))    m = mid;
        else M = mid;
    }
    printf("%0.10lf\n",m);
    return 0;
}