Which country does Mary Smith live in?
SELECT T3.country FROM address AS T1 INNER JOIN city AS T2 ON T1.city_id = T2.city_id INNER JOIN country AS T3 ON T2.country_id = T3.country_id INNER JOIN customer AS T4 ON T1.address_id = T4.address_id WHERE T4.first_name = 'MARY' AND T4.last_name = 'SMITH'