let conv = Bytes.map (fun x -> if 'A' <= x && x <= 'Z' 
                                  then Char.chr (Char.code x - Char.code 'A' + Char.code 'a')
                                  else if 'a' <= x && x <= 'z' then Char.chr (Char.code x - Char.code 'a' + Char.code 'A')
                                  else x)

let () =
  Printf.printf "%s\n" (Scanf.scanf "%s\n" (fun x -> conv x))