(defun replace-treeone-with-forest (s pre-str post-str)
  (let* ((search-str pre-str)
         (replace-str post-str)
         (search-len (length search-str))
         (result "")
         (start 0)
         (pos (search search-str s :start2 start)))
    (loop while pos
          do (setq result (concatenate 'string result (subseq s start pos) replace-str))
             (setq start (+ pos search-len))
             (setq pos (search search-str s :start2 start)))
    (concatenate 'string result (subseq s start))))

(defun main ()
  (princ (replace-treeone-with-forest (read-line) "treeone" "forest"))
  (terpri))
(main)