#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <string>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <cstring>

typedef long long ll;
using namespace std;

#define mod 1000000009
#define INF 10000000
#define LLINF 2000000000000000000LL

#define SIZE 10001

ll k;
int n,l[200000];

bool check(double p){
    ll cc=0;
    
    for(int i=0;i<n;i++)
        cc+=(int)(l[i]/p);
    
    return cc>=k;
}

int main(){
    scanf("%d",&n);
    
    for(int i=0;i<n;i++) scanf("%d",&l[i]);
    
    scanf("%lld",&k);
    
    double l=0,r=1000000000,mid;
    
    while(r-l>1e-10){
        mid = (l+r)/2;
        
        if(check(mid)){
            l = mid;
        }else{
            r = mid;
        }
    }
    
    printf("%.10lf\n",mid);
    
    return 0;
}