An internet access provider (IAP) owns two servers. Each server has a 50% chance of being "down" independently of the other. Fortunately, only one server is necessary to allow the IAP to provide service to its customers, i.e., only one server is needed to keep the IAP's system up. Suppose a customer tries to access the internet on four different occasions, which are sufficiently spaced apart in time, so that we may assume that the states of the system corresponding to these four occasions are independent. What is the probability that the customer will only be able to access the internet on 3 out of the 4 occasions?