let string_1_list_of_string x =
  String.to_seq x
  |> List.of_seq
  |> List.map (String.make 1);;

let rec solve result one two =
  let h1 = List.hd one in
  let h2 = List.hd two in
  let result = if (h1 <> "0") && (h2 <> "0") then result + 1 else result in
  match (List.length two) with
  | 1 -> result
  | _ -> solve result (one @ [h2]) (List.tl two);;

let () =
  let raw = read_line () |> string_1_list_of_string in
  let hd = [List.hd raw] in
  let tl = List.tl raw in
  solve 0 hd tl |> print_int; print_newline ();;