Question

Mr. Wilson and one man got on a streetcar. At the secong stop three people got on. At the third stop, three people got on and one got off. At the fourth stop, three got off. At the fifth stop, six people got off. At the sixth stop, one-half of the passengers got off and Mr. Wilson was the only passenger left on the the streetcar. How many passengers were on the streetcar when Mr. Wilson got on?