defmodule Main do
  def main do
    n=IO.gets("") |> String.trim() |> String.to_integer()
    1..n
    |>Enum.map(fn x->
      y=Integer.floor_div(n,x)
      y*(y+1)*x/2
    end)
    |>Enum.sum()
    |>Float.to_string()
    |>String.split(".")
    |>List.first()
    |>IO.puts()

  end
end
