package main

import (
	"bufio"
	"fmt"
	"os"
)

var sc = bufio.NewScanner(os.Stdin)

// 任意の要素数の文字列を読み込んでスライスで返す
func scanStrings(len int) (strings []string) {
	var str string
	for i := 0; i < len; i++ {
		fmt.Scanf("%s", &str)
		strings = append(strings, str)
	}
	return
}

// 任意の要素数の配列を読み込んでスライスで返す
func scanNums(len int) (nums []int) {
	var num int
	for i := 0; i < len; i++ {
		fmt.Scan(&num)
		nums = append(nums, num)
	}
	return
}

func reverse(s string) string {
	runes := []rune(s)
	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
		runes[i], runes[j] = runes[j], runes[i]
	}
	return string(runes)
}

func flag(mid float64, k int, ll []int) bool {
	sum := 0
	for _, v := range ll {
		sum += int(float64(v) / mid)
	}
	// fmt.Println("sum:", sum)
	if sum >= k {
		return true
	}
	return false
}

func main() {
	n := scanNums(1)[0]
	ll := scanNums(n)
	k := scanNums(1)[0]

	l := 0.0
	r := 1e10
	for i := 0; i < 100 && r-l > 1e-10; i++ {
		mid := (r + l) / 2.0
		if flag(mid, k, ll) {
			l = mid
			// fmt.Println("true mid:", mid)
		} else {
			r = mid
		}
	}

	// fmt.Println("n,l,k,ll", n, l, k, ll)
	fmt.Printf("%f\n", l)
}