Default value in interactive mode

[Heime]

How can I apply the default when user just enters RET 
to the interactive part?

(defun svem-nchar (&optional n)
  "Highlight the Nth character in the current word."

  (interactive "nWhich character to highlight (1-based): ")

  (let* ( (n            (or n 5))
          (brackets     "[](){}")
          (word-bounds  (bounds-of-thing-at-point 'word))
          (word-start   (car word-bounds))
          (word-end     (cdr word-bounds))
          (word         (buffer-substring word-start word-end))
          (char-count   0)
          (pos          word-start) )