CREATE TABLE table_name_35 (example_code__huc_ INTEGER, level VARCHAR(255), example_name VARCHAR(255), digits VARCHAR(255))
What is the mean huc example code when the example name's lower snake, there are 6 digits, and less than 3 levels?
    
SQL: SELECT AVG(example_code__huc_) FROM table_name_35 WHERE example_name = "lower snake" AND digits = 6 AND level < 3