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_21791 ( "Rank" real, "Country" text, "Miss United Continent" real, "Virreina" real, "1st RU" real, "2nd RU" real, "3rd RU" real, "4th RU" real, "Semifinalists" real, "Total" real )

### Question ###
How many 3rd ru does Canada have?

### Accurate SQL ###

SELECT COUNT("3rd RU") FROM table_21791 WHERE "Country" = 'Canada'