defmodule Main do
  def input, do: IO.read(:line) |> String.trim
  def ii, do: input() |> String.to_integer
  def li, do: input() |> String.split |> Enum.map(&String.to_integer/1)

  def digital_root(0), do: 0
  def digital_root(x) when x > 0 do
    case rem(x, 9) do
      0 -> 9
      n -> n
    end
  end

  def main do
    n = ii()

    IO.puts digital_root(n)
  end
end