#define _USE_MATH_DEFINES
 
#include <iostream>
#include <iomanip>
#include <sstream>
 
#include <algorithm>
#include <cmath>
 
#include <string>
//#include <array>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>
#include <map>
 
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
 
#define PII pair<int,int>
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////
LL N;
LL K;
LL Len[200000+1];
LL Lmin,Lmax;

LL f(LD norLen ){
	LL res = 0;
	rep(i,N){
		res += Len[i] / norLen;
	}
	return res;
}

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    cout << setprecision(16);//
	
	cin>>N;
	Lmax = 0;
	Lmin = (int)1e9;

	rep(i,N){
		cin>>Len[i];
		Lmax = max( Lmax, Len[i] );
		Lmin = min( Lmin, Len[i] );
	}
	cin>>K;
	if( 1 == N){
		P( (LD)Len[0]/K );
		return 0;
	}
	LD Right,Left,mid;
	LD pr,pl;
	LL temp;
	//２分探索
	Right = Lmax;
	Left = 0;
	mid = (Right+Left) / 2;
	pr = -1;
	pl = -1;
	//while( Right-Left > 0.0000000009 ){
	while( pr != Right || pl != Left ){
		pr = Right;
		pl = Left;
		mid = (Right+Left) / 2;
		temp = f( mid );
		if( temp >= K ){
			Left = mid;
		}else{// if( K > temp ){
			Right = mid;
		}
	}
	
	P( Left );


	return 0;
}