A grade: { }
B grade: { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 22, 24, 28, 29, 30, 32, 34, 35, 38, 40, 43, 45, 48, 49, 50 }
C grade: { }
F grade: { 17, 19, 20, 21, 23, 25, 26, 27, 31, 33, 36, 37, 39, 41, 42, 44, 46, 47, 51, 52, 53 }