let solve str =
    let len_str = String.length str in
    let rec solve' idx acc =
        if idx >= len_str then
            acc
        else
            let idx' = idx + 1
            and acc' = if str.[idx] = '0' then acc else acc + 1
            in
            solve' idx' acc'
    in
    solve' 1 0

let () =
    let str = read_line () in
    Printf.printf "%d\n" @@ solve str