#include <bits/stdc++.h>
using namespace std;

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FORR(x,arr) for(auto&& x:arr)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,a,b) for (int i = (b)-1; i >= (a); i--)
#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define ALL(x) (x).begin(), (x).end()
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define RITR(x,c) for(__typeof(c.rbegin()) x=c.rbegin();x!=c.rend();x++)
#define BIT(n) (1LL<<(n))
#define SZ(x) ((int)(x).size())
typedef long long ll;
// -------------------------------------

ll N, K;
int L[201010];

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

  cin >> N;
  int ma = 0;
  REP(i, N) {
    cin >> L[i];
    ma = max(ma, L[i]);
  }
  cin >> K;

  double l = 1.0 * L[0] / K;
  double r = ma+1;

  REP(_, 60) {
    double m = (l + r) / 2;
    ll n = 0;
    REP(i, N) {
      n += (ll) (L[i] / m);
    }
    if (n >= K) l = m;
    else r = m;
  }

  _P("%.10f\n", (l + r) / 2);

  return 0;
}