local mmi, mma, mfl = math.min, math.max, math.floor
local n = io.read("*n", "*l")
local str = io.read()
local ls = {}
local lmin, lmax = 0, 0
local ti = 1
for v in str:gmatch("%d+") do
  local num = tonumber(v)
  if lmax == 0 then
    lmin, lmax = num, num
  else
    lmin, lmax = mmi(lmin, num), mma(lmax, num)
  end
  ls[ti] = num
  ti = ti + 1
end
local k = io.read("*n")

local function check(tgt)
  local cnt = 0
  for i = 1, n do
    cnt = cnt + mfl(ls[i] / tgt)
  end
  return k <= cnt
end

local min, max = lmin / k, lmax
--while 1.0e-10 < max - min do
for i = 1, 500 do
  local mid = (min + max) / 2
  if check(mid) then
    min = mid
  else
    max = mid
  end
end
print(string.format("%.11f", (min + max) / 2))