How can we get an optimized surface in cl-sdl2?

(let* ((SURFACE (sdl2:load-bmp "/home/huseyin/quicklisp/local-projects/sdl2-made-easy/assets/gods.bmp"))

(OPTIMIZED-SURFACE (sdl2:convert-surface SURFACE sdl2:+pixelformat-

unknown+)))

as i understand, in order to get an optimized surface the second argument of "sdl2:convert-surface" must be one of many constants in "constants.lisp" file:

(defconstant +pixelformat-unknown+ sdl2-ffi:+sdl-pixelformat-unknown+)

(defconstant +pixelformat-index1lsb+ sdl2-ffi:+sdl-pixelformat-index1lsb+)

(defconstant +pixelformat-index1msb+ sdl2-ffi:+sdl-pixelformat-index1msb+)

...

Here i choosed the first one because i have no idea which one i must choose.

Is that enough in order to get an optimized surface in cl-sdl2?