Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_149426_4 (prefix_size VARCHAR, network_mask VARCHAR)

### Question ###
When the network mask is 255.255.255.252 what is the prefix size?

### Accurate SQL ###

SELECT prefix_size FROM table_149426_4 WHERE network_mask = "255.255.255.252"