#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <sstream>
#include <fstream>
#include <random>

#define REP(i, n) for (int (i) = 0; (i) < (n); (i)++)
#define FOR(i, a, b) for (int (i) = (a); (i) < (b); (i)++)
#define RREP(i, a) for (int (i) = (a) - 1; (i) >= 0; (i)--)
#define FORR(i, a, b) for (int (i) = (a) - 1; (i) >= (b); (i)--)
#define PI acos(-1.0)
#define DEBUG(C) cerr << C << endl;
#define VI vector <int>
#define VII vector <VI>
#define VL vector <LL>
#define VLL vector <VL>
#define VD vector <double>
#define VDD vector <VD>
#define PII pair <int, int>
#define PDD pair <double, double>
#define PLL pair <LL, LL>
#define VPII vector <PII>
#define ALL(a) (a).begin(), (a).end()
#define SORT(a) sort(ALL(a))
#define REVERSE(a) reverse(ALL(a))
#define MP make_pair
#define EB emplace_back
#define FORE(a, b) for (auto &&a : b)
#define FIND(s, n) (s.find(n) != s.end())

using namespace std;
typedef long long LL;
typedef unsigned long long ULL;
const int INF = 1e9;
const int MOD = INF + 7;
const LL LLINF = 1e18;

int N, K;
VL L;

bool check(double S) {
	int cnt = 0;
	FORE(el, L) cnt += el / S;
	return cnt >= K;
}

int main(void) {
	cin >> N;
	L.resize(N);
	REP(i, N) scanf("%lld", &L[i]);
	cin >> K;
	double high = 1e11, low = 0.0;
	REP(_, 1000) {
		double mid = (high + low) / 2;
		//double mid = low + (high - low) / 2;
		(check(mid) ? low : high) = mid;
	}
	cout << fixed << setprecision(15) << low << endl;
}