Write SQL query to solve given problem: How many times more was the number of students of University of Ottawa than Joseph Fourier University in 2013?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE WHEN T2.university_name = 'University of Ottawa' THEN T1.num_students ELSE 0 END) AS REAL) / SUM(CASE WHEN T2.university_name = 'Joseph Fourier University' THEN T1.num_students ELSE 0 END) FROM university_year AS T1 INNER JOIN university AS T2 ON T1.university_id = T2.id WHERE T1.year = 2013