import std.algorithm, std.array, std.container, std.range, std.bitmanip;
import std.numeric, std.math, std.bigint, std.random, core.bitop;
import std.string, std.conv, std.stdio, std.typecons;

void main()
{
  auto n = readln.chomp.to!long;
  auto li = readln.split.map!(to!long);
  auto k = readln.chomp.to!long;

  auto maxL = li.reduce!(max);

  bool calc(real x, real _) {
    long c = 0;
    foreach (l; li) {
      auto d = (l / x).floor;
      if (d >= long.max || d >= long.max - c || c + d >= k)
        return true;
      c += d.to!long;
    }
    return c >= k;
  }

  auto eps = 10.to!real ^^ (-10);
  auto r = iota(eps, maxL, eps).assumeSorted!(calc).lowerBound(0);
  writefln("%.9f", r.back);
}