Table: `Courses`

    +-------------+---------+
    | Column Name | Type    |
    +-------------+---------+
    | student     | varchar |
    | class       | varchar |
    +-------------+---------+
    (student, class) is the primary key column for this table.
    Each row of this table indicates the name of a student and the class in which they are enrolled.

Write an SQL query to report all the classes that have at least five students.

Return the result table in any order.

The query result format is in the following example.

Example 1:

    Input:
    Courses table:
    +---------+----------+
    | student | class    |
    +---------+----------+
    | A       | Math     |
    | B       | English  |
    | C       | Math     |
    | D       | Biology  |
    | E       | Math     |
    | F       | Computer |
    | G       | Math     |
    | H       | Math     |
    | I       | Math     |
    +---------+----------+
    Output:
    +---------+
    | class   |
    +---------+
    | Math    |
    +---------+
    Explanation:
    - Math has 6 students, so we include it.
    - English has 1 student, so we do not include it.
    - Biology has 1 student, so we do not include it.
    - Computer has 1 student, so we do not include it.