How many Mountains Classifications were in the race with Mike Northey as Youth Classification?
CREATE TABLE table_23157997_13 (
    mountains_classification VARCHAR,
    youth_classification VARCHAR
)
SELECT COUNT(mountains_classification) FROM table_23157997_13 WHERE youth_classification = "Mike Northey"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How many Mountains Classifications were in the race with Mike Northey as Youth Classification? ### Input: CREATE TABLE table_23157997_13 (
    mountains_classification VARCHAR,
    youth_classification VARCHAR
) ### Response: SELECT COUNT(mountains_classification) FROM table_23157997_13 WHERE youth_classification = "Mike Northey"