public static long S5(){
		long numS5 = 0;
		// S5: No student should write exams with no break between them
		for(Student s : Environment.get().students.objects()){
			for(Lecture l1 : s.lectures){
				if(l1.session == null) continue;
				for(Lecture l2 : s.lectures){
					if(l2.session == null) continue;
					// lecture session days should not be null!
					assert l1.session.day != null;
					assert l2.session.day != null;
					
					// student attends two different lectures with exams on the same day
					if(l1 != l2 && l1.session.day.equals(l2.session.day)){
						// lecture session times should never be null!
						assert l1.session.time != null;
						assert l2.session.time != null;
						if(l1.session.time <= l2.session.time){
							// examlength cannot be null
							assert l1.examLength != null;							
							// next exam starts without break!
							if(l1.examLength + l1.session.time == l2.session.time){
								//System.out.println("Found S5: " + l1.getName() + " " + l2.getName());
								numS5++;
							}
						} 
					}
				}
			}
		}
		return  numS5;
	}