defmodule Main do
  def main do
    [n, k] = IO.read(:line) |> String.trim() |> String.split(" ") |> Enum.map(&String.to_integer/1)
    solve(n, k) |> IO.puts()
  end

  def solve(n, k) when 1 <= n and n <= 100_000
    and 1 <= k and k <= 100_000
  do
    0..n
    |> Enum.reduce({0, 0}, fn ni, {sum, count} ->
      ki = 0..k |> Enum.count
      {sum + ni * ki, count + ki}
    end)
    |> (fn {sum, count} ->
      sum / count
    end).()
  end
end