one-way or round trip for Mutianyu Great Wall

Hi!

Our intention is to go to tower 14 by cablecar, hike up to 23 and then go back to 6 to go down the slideway but we don't know if we will have time or will be too tired on the way.
My question is, is it possible to buy a round-trip and then decide if we want to go down by cable car or slideway? Or will we have to buy separate tickets?