What's the number of users gave the movie "Downfall" a rating of "4"?
movie "Downfall" refers to movie_title = 'Downfall'; rating of "4" refers to rating_score = 4
SELECT COUNT(T1.user_id) FROM ratings AS T1 INNER JOIN movies AS T2 ON T1.movie_id = T2.movie_id WHERE T2.movie_title = 'Downfall' AND T1.rating_score = 4