Passage: After the 2002 completion of Insomnia, Nolan presented to Warner Bros. a written 80-page treatment about a horror film envisioning "dream stealers" based on lucid dreaming. Deciding he needed more experience before tackling a production of this magnitude and complexity, Nolan retired the project and instead worked on 2005's Batman Begins, 2006's The Prestige, and The Dark Knight in 2008. The treatment was revised over 6 months and was purchased by Warner in February 2009. Inception was filmed in six countries, beginning in Tokyo on June 19 and ending in Canada on November 22. Its official budget was US$160 million, split between Warner Bros and Legendary. Nolan's reputation and success with The Dark Knight helped secure the film's US$100 million in advertising expenditure.

Question: How many countries was Inception filmrd in?
six countries