The horney sister

You ,Zee, are checking on your older sister, Faith, to see if she is awake yet so you two can play basketball. Honestly the only reason you want to play basketball is to see Faiths huge and well shaped boobs bouncing when she jumps to make a basket. Faith has a slim body, huge boobs, and tight ass that you admire. You lightly knock on the door receiving no answer. You open the door slightly and see Faith on her bed with her back arched and her fingers penetrating her pussy. You already have a boner. But you just cant stand here in the middle of the hallway jacking off. What will you do?