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_13641 ( "Stage" text, "Winner" text, "General classification" text, "Points classification" text, "Mountains classification" text, "Young rider classification" text )

### Question ###
What's the points classification of Stage 18 when the general classification was Denis Menchov?

### Accurate SQL ###

SELECT "Points classification" FROM table_13641 WHERE "General classification" = 'denis menchov' AND "Stage" = '18'