user: Question: What is the sum of Silver when the total is less than 6, the rank is 6 and the Bulgaria is the nation?
Columns: ['Rank', 'Nation', 'Gold', 'Silver', 'Bronze', 'Total']
Types: ['text', 'text', 'real', 'real', 'real', 'real']
Sample row: ['1', 'Russia', 6.0, 5.0, 5.0, 16.0]
SQL:

assistant: SELECT SUM("Silver") FROM "Table" WHERE "Total" < 6.0 AND "Rank" = '6' AND "Nation" = 'Bulgaria';