n=30;
grades=[|78,51,71|
41,59,72|
34,62,31|
56,74,37|
81,96,92|
58,37,80|
94,58,59|
98,84,84|
80,44,34|
44,35,97|
95,96,94|
76,41,86|
88,42,57|
84,89,84|
75,43,98|
31,48,61|
95,96,93|
72,46,47|
61,85,49|
81,69,42|
71,56,88|
97,77,93|
87,92,92|
38,85,55|
56,53,46|
52,89,33|
48,38,82|
69,60,31|
93,96,92|
85,36,99|];