University of Notre Dame
The residence halls, or dorms, are the focus of the student social and intramural life. About 80 percent of undergraduates and 20 percent of graduate students live on campus. Each of the 30 undergraduate residence halls has its own colors, mascot, sport teams, signature events, traditions, and lore. Residence halls range in population from the largest (Dillon Hall) with 332 undergraduates to the smallest (Carroll Hall) with only 100 undergraduates. The halls are single-sex, with 16 male dorms and 14 female dorms, and Old College, a house of formation for male college students discerning entrance into the Congregation of Holy Cross. The university maintains a visiting policy (known as parietal hours) for those students who live in dormitories, specifying times when members of the opposite sex are allowed to visit other students' dorm rooms; however, all residence halls have 24-hour social spaces for students regardless of sex. Instead, the majority of the graduate students on campus live in one of four graduate housing complexes on campus Each hall is led by a rector, a full-time, live-in professional who serves as leader, chief administrator, community builder and university resources to the residents, and is either a priest, religious sister or brother, or layperson trained in ministry and/or education. Rectors direct the hall community, foster bonding, and often coordinate with professors, academic advisors, and counselors to watch over students and assist them with their personal development. Rectors select, hire, train, and supervise hall staff: resident assistants (required to be seniors) and assistant rectors (graduate students). Many residence halls also have a priest or faculty members in residence as faculty fellows, who provide an additional academic and intellectual experience to residential hall life. Every hall has its own chapel, dedicated to the hall's patron saint, and liturgical schedule with masses celebrated multiple times a week during the academic year, in the tradition of individual chapels at English university colleges.
University of Notre Dame
Fraternities and sororities are not allowed on campus, as they are described as in opposition to the University's educational and residential mission. The residential halls provide the social and communal aspect of fraternities, but in line with the university's policy of inclusion and zero tolerance of hazing, and according to former Director of Admissions Dan Saracino without "any of the disadvantages [of the Greek system] – rush, the cliques, deciding on whether you're good enough to join them, monthly ‘dues’ and a much lower diversity of people living together”.Over four-fifths of students live in the same residence hall for three consecutive years and about one-third of students live in the same residence hall for all four years s of October 2017 . A new policy was put into effect which requires undergraduate students to live on-campus for three years starting in 2018. In spring 2019 the university also announced a policy that prohibits students living off-campus from participating in dorm activities such as intramural sports and dorm dances. Most intramural (interhall) sports are based on residence hall teams, where the university offers the only non-military academy program of full-contact intramural American football. At the end of the interhall football season, the championship game is played in Notre Dame Stadium.

Question: How many student housing areas are reserved for Notre Dame's graduate students?
Answer: four