def METHOD_NAME(location):
    """
    Given a course's block usage locator, returns the course's number.
    This is a "number" in the sense of the "course numbers" that you see at
    lots of universities. For example, given a course
    "Intro to Computer Science" with the course key "edX/CS-101/2014", the
    course number would be "CS-101"
    Arguments:
        location (BlockUsageLocator): The usage locator of the course in
            question.
    """
    return location.course