Not sure what 3 meant but since you replied let me give you information on other causes plus medication you might use.
To help your dog breathe easier, Robitussin DM at a 1/4 teaspoon per 5 pounds can be used to control the cough. It should only contain dextromethorphan and Guaifenisen. and should NOT contain pseudoephedrine. If your dog has not had a vet visit in a while or a heart condition is suspected you should not give Robitussin until it is ruled out as it can mask heart issues. Dosages can be obtained at this website.
Other causes of cough includes bronchitis. You can read about bronchitis here:
Inhaled allergies can also cause coughs.
Here is a website with more information on kennel cough. http://www.peteducation.com/article.cfm?c=2+2096&aid=452
Canine influenza is now becoming more prevalent and like it sounds it is a canine flu. Here is an excellent site on it.
There are other reasons for coughs such as heart problems which should be investigated if your dog is not on heartworm preventative or is an older dog. The following site goes over canine coughs.
Your dog could be doing what is called a reverse sneeze or a collapsing trachea. Here is a site on reverse sneezes and one on collapsing tracheas.
I do hope the cough resolves pretty quickly.