#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <climits>
#include <algorithm>
#include <cmath>
#include <cstdlib>
#include <stack>
#include <queue>
#include <string>
#include <map>
#include <set>
#include <sstream>
#include <functional>
#include <ctime>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n)  FOR(i,0,n)
#define CLEAR(d) memset((d), 0, (sizeof((d))))
#define ALL(c) (c).begin(), (c).end()
#define ABS(x) ((x < 0) ? -(x) : (x))
#define SORT(x) sort((x).begin(), (x).end())
#define RSORT(x) sort((x).begin(), (x).end(), greater<int>() )
#define SIZE(a) ((int)((a).size()))
#define MAX3(a, b, c) (max(max((a), (b)), (c)))
#define MIN3(a, b, c) (min(min((a), (b)), (c)))
#define MOD 1000000007
#define EPS 1e-5
#define PI  (acos(-1))
#define INF 10000000
//===================================================

int main()
{
    int n;
    ll k, sum = 0;
    cin >> n;
    vector<int> l(n);
    REP(i, n) cin >> l[i];
    cin >> k;
    double lb = 0, ub = 1000000000, mid = 0, div = 0;
    REP(i,300) {
        mid = (ub + lb) / 2;
        div = 1.0 / mid;
        sum = 0;
        REP(j, n) sum += (ll)(l[j] * div);
        if (sum >= k) {
            lb = mid;
        }
        else {
            ub = mid;
        }
    }
    printf("%.10f\n", (ub + lb) / 2);
    return 0;
}