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_name_21 (laps INTEGER, time_retired VARCHAR, grid VARCHAR)

### Question ###
Tell me the sum of laps with a time/retired of +13 laps with grid more than 18

### Accurate SQL ###

SELECT SUM(laps) FROM table_name_21 WHERE time_retired = "+13 laps" AND grid > 18