SCHEMA:
CREATE TABLE table_name_16 (assets__us INTEGER, company VARCHAR, revenues__us$_billion_ VARCHAR)
USER:
What are the smallest assets with a Company of piraeus bank, and a Revenue (US$ billion) smaller than 3.9?

QUERY:
SELECT MIN(assets__us) AS $_billion_ FROM table_name_16 WHERE company = "piraeus bank" AND revenues__us$_billion_ < 3.9