let shift s =
  String.map (fun c ->
      let cc = (Char.code c) in
      if cc >= 97 && cc <= 122 then (cc - 96) mod 26 |> (+) 97 |> Char.chr
      else c) s;;
let reg = Str.regexp "this\\|the\\|that";;

let rec read u =
  try let line = read_line () in
      let rec find l =
        if Str.string_match reg l 0 then print_endline l
        else shift l |> find
      in find line;read u
  with
    End_of_file -> ()
    in read ();;