#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int (i) = 0 ; (i) < (int)(n) ; (i)++)
#define REP(i,a,b) for(int (i) = a ; (int)(i) <= (int)(b) ; (i)++)
#define all(n) (n).begin(),(n).end()
typedef long long ll;
typedef vector<int> Vi;
typedef vector<Vi> VVi;
typedef pair<long long,long long> Pii;
typedef vector<Pii> VPii;
typedef complex<double> P;

int L[200010];
int main(){
	int N;
	cin >> N;
	for(int i = 0 ; i < N ; i++) cin >> L[i];
	double l = 0 , r = 1e9;
	long long K;
	cin >> K;
	rep(_,128){
		double m = (l+r) / 2;
		
		long long sum = 0;
		rep(i,N) sum += (long long)(L[i] / m);
		if( sum >= K ){
			l = m;
		}else{
			r = m;
		}
	}
	printf("%.10lf\n",r);
}