Scanf.scanf "%s" (fun s ->
    let n = String.length s in
    let rec loop i sum =
        if i = n then sum else
            let sum = if s.[i] >= '1' && s.[i] <= '9' then sum + int_of_char s.[i] - 48 else sum in
            loop (i + 1) sum
    in
    loop 0 0 |> Printf.printf "%d\n"
)