user: Question: What is the fewest number of silvers for teams with more than 21 gold and more than 4 bronze?
Columns: ['Rank', 'Institution', 'Gold', 'Silver', 'Bronze']
Types: ['text', 'text', 'real', 'real', 'real']
Sample row: ['1', 'University of Texas at Austin', 7.0, 2.0, 1.0]
SQL:

assistant: SELECT MIN("Silver") FROM "Table" WHERE "Bronze" > 4.0 AND "Gold" > 21.0;