A pair of fair dice are tossed until a sum of eight appears for the first time. What is the probability that more than four rolls will be required for that to happen?

I figured that the probability that the sum is 8 is 5/36 on one throw from the choices {(2,6)(3,5)(4,4)(5,3)(6,2)} I'm not sure how to find the probability that more than 4 rolls are needed to get the sum 8 though. Can someone help?