2, 4
2, 4, 1, 10, 14, 16, 18, 19, 2, 20, 21, 22, 25, 28, 29, 30, 31, 33, 34, 36, 37, 39, 4, 40, 41, 42, 44, 48, 5, 50, 6, 7