Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_15 ( mountains_classification VARCHAR, general_classification VARCHAR, winner VARCHAR )

### Question ###
What's the mountains classification of winner Carlos Sastre when the general classification is Denis Menchov?

### Accurate SQL ###

SELECT mountains_classification FROM table_name_15 WHERE general_classification = "denis menchov" AND winner = "carlos sastre"