#include <iostream>
using namespace std;

int L[200010];
int main(){
    int N;
    cin >> N;
    
    for(int i=0;i<N;i++)cin >> L[i];
    
    int K;
    cin >> K;
    
    double lo = 0, hi = 1000000010;
    for(int i=0;i<100;i++){
        double mid = (lo + hi) / 2;
        int ks = 0;
        
        for(int i=0;i<N;i++){
            ks += L[i] / mid;
        }
        
        if(ks >= K){
            lo = mid;
        } else {
            hi = mid;
        }
    }
    
    printf("%.15f\n", lo);
    return 0;
}