let () =
  let rec charlist_of_string str n i =
    if i = n then [] else str.[i] :: charlist_of_string str n (i+1) in
  let rec convert lst = match lst with
    | [] -> ""
    | h :: t ->
      if h = Char.lowercase_ascii h then (Char.escaped (Char.uppercase_ascii h)) ^ convert t
      else (Char.escaped (Char.lowercase_ascii h)) ^ convert t in
  Scanf.scanf "%s\n" @@ fun s ->
  let lst = charlist_of_string s (String.length s) 0 in
  Printf.printf "%s\n" (convert lst)