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 f(x) do
    if x == 0 do
      0
    else
      case rem(x, 9) do
        0 -> 9
        n -> n
      end
    end
  end

  def main do
    n = ii()

    IO.puts f(n)
  end
end