#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>

#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
typedef long long ll;

using namespace std;


int inputValue(){
    int a;
    cin >> a;
    return a;
};

void inputArray(int * p, int a){
    rep(i, a){
        cin >> p[i];
    }
};

void inputVector(vector<int> * p, int a){
    rep(i, a){
        int input;
        cin >> input;
        p -> push_back(input);
    }
}

template <typename T>
void output(T a, int precision) {
    if(precision > 0){
        cout << setprecision(precision)  << a << "\n";
    }
    else{
        cout << a << "\n";
    }
}

ll L[210000] = {0};

int main(int argc, const char * argv[]) {
    
    // source code
    int N = inputValue();
    rep(i, N){
        L[i] = inputValue();
    }
    ll K = inputValue();
    
    
    double high = 1e10;
    double low = 0.0;
    double mid = 1e10;
    
    rep(i, 120){
        ll count = 0;
        rep(j, N){
            count += (long long)(L[j] / mid);
        }
        if(count >= K){
            low = mid;
            mid = (mid + high) / 2;
        }
        if(count < K){
            high = mid;
            mid = (mid + low) / 2;
            
        }
    }
    
    printf("%.11f\n", mid);
    
    
    
    return 0;
}