#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

ll N, K;
ll L[200000];

bool solve(double l) {
	ll rem = K;
	REP(i, N) {
		rem -= (int)(L[i] / l);
	}
	return rem <= 0;
}

int main(int argc, char **argv) {
	cin >> N;
	REP(i, N) cin >> L[i];
	cin >> K;
	double l = 0.0, r = 1e9;
	REP(i, 200) {
		double m = (l + r) / 2;
		if (solve(m)) l = m;
		else r = m;
	}
	double res = (l + r) / 2;
	cout << fixed << setprecision(10) << res << endl;
	return 0;
}