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_16431 ( "Rnd" real, "Race Name" text, "Pole position" text, "Fastest lap" text, "Winning driver" text, "Winning team" text, "Report" text )

### Question ###
In Round 6, how many winning drivers were there?

### Accurate SQL ###

SELECT COUNT("Winning driver") FROM table_16431 WHERE "Rnd" = '6'