In Round 6, how many winning drivers were there?
CREATE TABLE table_16431 (
    "Rnd" real,
    "Race Name" text,
    "Pole position" text,
    "Fastest lap" text,
    "Winning driver" text,
    "Winning team" text,
    "Report" text
)
SELECT COUNT("Winning driver") FROM table_16431 WHERE "Rnd" = '6'
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: In Round 6, how many winning drivers were there? ### Input: CREATE TABLE table_16431 (
    "Rnd" real,
    "Race Name" text,
    "Pole position" text,
    "Fastest lap" text,
    "Winning driver" text,
    "Winning team" text,
    "Report" text
) ### Response: SELECT COUNT("Winning driver") FROM table_16431 WHERE "Rnd" = '6'