type case = Lower | Upper | Other

let case_of_char c =
  if 'a' <= c && c <= 'z' then Lower
  else if 'A' <= c && c <= 'Z' then Upper
  else Other

let solve s =
  let buf = Bytes.of_string s in
  let blen = Bytes.length buf in
  let rec solve' idx =
    if idx < blen then (
      let c = buf.[idx] in
      let cc = match case_of_char c with
      | Lower -> Char.uppercase c
      | Upper -> Char.lowercase c
      | Other -> failwith "hoge"
      in
      Bytes.set buf idx cc;
      solve' (idx + 1)
    )
  in solve' 0;
  Bytes.to_string buf

let () =
  let s = read_line () in
  solve s |> print_endline