# initial database
1, aa, 8.2, 5
560, 39
450, 58
620, 76
470, 49
520, 78
2, ab, 6.7, 3
560, 45
450, 50
620, 60
3, ac, 5.9, 2
560, 39
450, 42
# add student
4, ad, 7.9, 3
5, ae, 7.1, 3
# add course
4, 520, 81
5, 560, 70
# modify student
1, 8.1
# modify course
5, 560, 76
# delete student
2
# delete course
1, 520