How many athletes took part in the Olympic games held in Barcelona?
Barcelona refers to city_name = 'Barcelona';
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 = 'Barcelona'