How many persons participated in the Sapporo Olympics?
the Sapporo Olympics refer to games_id where city_name = 'Sapporo';
SELECT COUNT(T1.person_id) FROM games_competitor AS T1 INNER JOIN games_city AS T2 ON T1.games_id = T2.games_id INNER JOIN city AS T3 ON T2.city_id = T3.id WHERE T3.city_name = 'Sapporo'