#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

const int MA = 200001;
int N, L[MA];
ll K;

int main(){
    cin >> N;
    rep(i, N)scanf("%d", &L[i]);
    cin >> K;
    double l = 0, r = 5e10, m;
    rep(i, 100){
        ll x = 0;
        m = (l + r) / 2;
        rep(j, N)x += (ll)(L[j] / m);
        (x >= K ? l : r) = m;
    }
    printf("%0.15f\n", l);
}