Scanf.scanf "%s" (fun s ->
    let n = String.length s in
    let rec loop i cur op acc =
        if i = n then (if op = '+' then acc * cur else acc + cur) else
            if s.[i] = '+' || s.[i] = '*' then (
                let acc = if op = '+' then acc * cur else acc + cur in
                loop (i + 1) 0 s.[i] acc
            ) else loop (i + 1) (cur * 10 + int_of_char s.[i] - 48) op acc
    in
    loop 0 0 ' ' 0 |> Printf.printf "%d\n"
)