defmodule Main do
  def main do
    n =
      IO.read(:line)
      |> String.trim
      |> String.to_integer

    ans =
      1 .. n + 1
      |> Enum.reduce(0, fn (i, acc) ->
        y = div(n, i)
        acc + div(y * (y + 1) * i, 2)
      end)


    IO.puts(ans)
  end
end
