SCHEMA:
CREATE TABLE table_12221135_3 (arrival VARCHAR, operator VARCHAR, calling_at VARCHAR)
USER:
How many trains call at Castor, Overton, Peterborough East and are operated by LNWR?

QUERY:
SELECT COUNT(arrival) FROM table_12221135_3 WHERE operator = "LNWR" AND calling_at = "Castor, Overton, Peterborough East"