Scanf.scanf "%d" (fun x ->
    let rec pat = 0 :: 0 :: 1 :: 1 :: 0 :: 1 :: 1 :: pat in

    let rec loop pos moved = function
        | [] -> failwith "??"
        | y :: ys ->
                let pos   = if y = 0 then pos   + 2 else pos - 1 in
                let moved = if y = 0 then moved + 2 else moved + 1 in
                if pos = x then moved else loop pos moved ys
    in
    loop 0 0 pat |> Printf.printf "%d\n"
)