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_63728 ( "Rank" real, "Nation" text, "Gold" real, "Silver" real, "Bronze" real, "Total" real )

### Question ###
What is the average bronze medal when gold is greater than 0, and there is less than 0 silver medals?

### Accurate SQL ###

SELECT AVG("Bronze") FROM table_63728 WHERE "Gold" > '0' AND "Silver" < '0'