1, 3, 2, -2, -1, 5, 4, -4, -3, 7, 6, -6, -5, 9, 8, -8, -7, 11, 10, -10, -9, 13, 12, -12, -11, 15, 14, -14, -13, 17, 16, -16, -15, 19, 18, -18, -17, 21, 20, -20, -19, 23, 22, -22, -21, 25, 24, -24, -23, 27, 26, -26, -25, 29, 28, -28, -27, 31, 30, -30, -29, 33