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 slen = String.length s in
  let rec solve' idx result =
    if idx >= slen then result
    else
      let c = s.[idx] in
      let nextC = match case_of_char c with
      | Lower -> Char.uppercase c
      | Upper -> Char.lowercase c
      | Other -> failwith "hoge"
      in
      solve' (idx + 1) (result ^ String.make 1 nextC)
  in solve' 0 ""

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