defmodule Main do
    def getsAll(device \\ :stdio, prompt), do: getsAll(device, prompt, "")
    defp getsAll(device, prompt, input) do
        x = IO.gets(device, prompt)
        case x do
            {:error, _} -> x
            :eof -> input
            _ -> getsAll(device, prompt, input <> x)
        end
    end
    def sum(n), do: sum(n, 1)
    defp sum(n, acc) do
        case n do
            1 -> acc
            _ -> sum(n - 1, acc + n)
        end
    end
    def main do

        inputs = getsAll(nil) |> String.split

        n = inputs |> Enum.at(0) |> String.to_integer

        IO.puts sum(n)

    end
end