2.1.9 Mathics

A grade: { 1, 3, 22 }

B grade: { 5 }

C grade: { 6, 19 }

F grade: { 2, 4, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 21, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 }