First, the sum of all the numbers in the clock is 12 * 13 / 2 = 78. So we know that each part has a sum of 26. Thinking about how the clock can be broken implies that there must be at least two parts containing consecutive numbers. Thus, we have (11, 12, 1, 2), (5, 6, 7, 8), and the rest: (3, 4, 9, 10).