I have noticed.
Despite the fact that the tasks are nice it is one of the worst contests I have ever participated in. After submitting the solution to the problem I have seen the message: "Submitted; Wrong answer on the sample case". However, on my machine the code worked on the sample case perfectly, so I tried a lot of understandings of what "sample case" is and even wrote one more solution. Eventually, by some asserts I have figured out that the "sample case" is the same as in the statement. But if it is so why my answer (which is completely the same as in the statement) is incorrect?! I tried a lot of approaches to output the answer, actually nothing worked. Now, it seems like a rejudge. Now my status for this problem is "Submitted; sample case solved correctly" which proves that it was not my fault. Though my status is "sample solved correctly", it has killed a lot of my nerves and spoiled the whole contest. Really, don't want to participate in USACO anymore because of these "guess the reason of WA" games.

There are easier ways to solve it even if you haven't seen heavy-light before. The problem is made more approachable by the fact that you can only query single edges of the tree.