def parse_viewed_courses(json):
    """
    Parse course viewed statements.

    Extract the students that have viewed the course from the course viewed statements.
    Return a list of those students.

    :param json: All the course viewed statements since a certain time.
    :type json: dict(str, str)
    :return: List of students who have viewed the course.
    :rtype: list(str)
    """
    student_list = []
    for statement in json['statements']:
        student_id = statement['actor']['account']['name']
        if student_id not in student_list:
            student_list.append(student_id)

    return student_list