Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_18 (bronze INTEGER, nation VARCHAR, silver VARCHAR)
### Question:
How many bronze medals for the United Kingdom when the silver was less than 0?
### Answer:
SELECT AVG(bronze) FROM table_name_18 WHERE nation = "united kingdom" AND silver < 0