#include <stdio.h>
#include <string.h>
#include <iostream>
#include <vector>
#include <deque>
#include <queue>
#include <stack>
#include <map>
#include <string>
#include <algorithm>
#include <numeric>
#include <utility>
#include <cmath>

using namespace std;

typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<int, int> pii;
typedef pair<ll, int> pli;

const int iinf = 1 << 29;
const long long linf = 1ll << 61;

#define dump(x) cerr << #x << " : " << x << '\n'
#define MOD(x, y) (((y) + (x) % (y)) % (y))

ll N, K;
double L[200000];

bool C(double x)
{
	ll i = 0;
	for (int j = 0; j < N; j++) {
		i += (int)(L[j] / x);
	}
	return i >= K;
}

int main(int argc, char* argv[])
{
	scanf("%lld", &N);
	for (int i = 0; i < N; i++) {
		scanf("%lf", &L[i]);
	}
	scanf("%lld", &K);

	double l = 0, u = (double)linf;
	for (int i = 0; i < 2000; i++) {
		double mid = (l + u) / 2;
		if (C(mid)) l = mid;
		else u = mid;
	}
	printf("%.14f\n", l);

	return 0;
}