#include <iostream>
#include <iomanip>

#define FORR(i,b,e) for(int i=(b);i<(int)(e);++i)
#define FOR(i,e) FORR(i,0,e)
#define dump(var) cerr << #var ": " << var << "\n"
#define dumpc(con) for(auto& e: con) cerr << e << " "; cerr<<"\n"

typedef long long ll;
typedef unsigned long long ull;

using namespace std;

int L[200010];

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);

    int N;
    ll K;
    double lmax = 0;
    cin >> N;
    FOR(i, N) {
        cin >> L[i];
        lmax += L[i];
    }
    cin >> K;
    lmax /= K;

    double l = 0.0, u = lmax, m;
    FOR(i, 50) {
        m = (l+u)/2;
        ll cnt = 0;
        FOR(j, N) {
            cnt += (ll)(L[j]/m);
        }
        if (cnt < K) {
            u = m;
        }
        else {
            l = m;
        }
    }
    cout << fixed << setprecision(10) << m << endl;
    
    return 0;
}