Expect two but be prepared for a third.. There is nothing you can do at this point other than wait it out. After the first two arrive do a belly check and feel for another or just wait it out. If all is going well there should have no more that 2 -2.5 hrs between pups. Just be sure that all placenta are accounted for. Two pups, two placentas or three pups three placentas. Its ok to let her eat one or two of them but if there is a third toss it out. To many can cause issue with bowels and upset.
Here is a site that will be very helpful:
Canine Reproduction Video and Book on Breeding and Whelping dogs by Debbie Jensen for dog breeders and Whelping Supplies needed to deliver puppies.