n=20;
grades=[|78,85,84|
90,50,39|
51,34,57|
87,83,35|
40,50,47|
34,55,58|
50,71,52|
49,64,69|
85,59,44|
73,46,95|
45,82,91|
95,99,96|
31,35,53|
84,70,85|
94,99,98|
37,76,40|
58,59,92|
41,43,45|
50,80,63|
62,48,68|];