module String = struct
  include String

  let fold_left f init str =
    let n = String.length str - 1 in
    let rec doit i acc =
      if i > n then acc
      else doit (i + 1) (f acc str.[i]) in
    doit 0 init

end

let () =
  read_line ()
  |> String.fold_left (fun s c -> s + Char.code c - Char.code '0') 0
  |> Printf.printf "%d\n"