#include <iostream>
#include <cstdio>
using namespace std;

int n, l[200005];
long long k;

bool C(double x){
    long long sum=0;
    for(int i=0; i<n; i++){
        sum += l[i] / x;
    }
    return sum >= k;
}
int main(void){
    cin >> n;
    for(int i=0; i<n; i++){
        cin >> l[i];
    }
    cin >> k;
    double left = 0;
    double right = 10000000010;
    for(int i=0; i<100; i++){
        double mid = (left+right)/2;
        if(C(mid)){
            left = mid;
        }else{
            right = mid;
        }
    }
    printf("%.10f",left);
    return 0;
}