# initial addition of database
2, aa, 8.2, 5
560, 39
450, 58
620, 76
470, 49
520, 78
3, ab, 6.7, 3
560, 45
450, 50
620, 60
4, ac, 5.9, 2
560, 39
450, 42
# add students
5, ad, 7.9, 2
# add course
5, 520, 81
# delete course
2, 560
# delete student
3
# modify course
2, 450, 88
# modify student
5, 8.9
# delete student
1
# delete course
2, 650
# modify student 
1, 6.5
# modify course
2, 650, 67
# add students
2, ae, 7.5, 4
# add course
4, 450, 86
# add students
1, af, 8.1, 2
3, ag, 8.4, 2
6, ah, 7.4, 1
# add course
5, 420, 59
5, 500, 45
5, 560, 70
6, 450, 85
1, 520, 68
1, 560, 80
3, 520, 70
3, 560, 76
# delete course
2, 470
2, 620
2, 450
# delete student
4
6
1