SCHEMA:
CREATE TABLE table_name_8 (silver INTEGER, bronze VARCHAR, gold VARCHAR, nation VARCHAR)
USER:
What is the average silver that has a gold greater than 3, with soviet union (urs) as the nation, and a bronze greater than 26?

QUERY:
SELECT AVG(silver) FROM table_name_8 WHERE gold > 3 AND nation = "soviet union (urs)" AND bronze > 26