#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    int N;
    cin>>N;
    VI L(N);
    FOR(i,N) scanf("%d",&L[i]);
    long long K;
    cin>>K;
    double lower = 0, upper = 1000000000;
    FOR(_,100){
        double l = (lower + upper) / 2;
        long long k = 0;
        FOR(i,N) k += L[i] / l;
        if(K <= k){
            lower = l;
        }else {
            upper = l;
        }
    }
    printf("%.10f\n", lower);
    return 0;
}