Saving a pointer to the n/4 node in AVL tree

Question

I have an AVL Tree which every node has a filed with a key which is an integer. I need to save a pointer to the Minimum , Maximum and the $\left \lfloor \frac{n}{4} \right \rfloor $ nodes. the first and the second were pretty easy i just saved a pointer between each node and its follow and back nodes. But i couldn't find a way to save the $\left \lfloor \frac{n}{4} \right \rfloor$ one. Any ideas? thank you.