CREATE TABLE table_name_16 (assets__us INTEGER, company VARCHAR(255), revenues__us$_billion_ VARCHAR(255))
What are the smallest assets with a Company of piraeus bank, and a Revenue (US$ billion) smaller than 3.9?
    
SQL: SELECT MIN(assets__us) AS $_billion_ FROM table_name_16 WHERE company = "piraeus bank" AND revenues__us$_billion_ < 3.9