Hello I managed to understand the problem and what it needs but my idea is to use Catalan numbers to count number of binary trees but in problem it wants to count the number of BS trees of length n with height at least h and root and leafs included but I could not discard or exclude all count of trees of height less than h from Catalan numbers

Any hint please I will be thankful and grateful and thanks in advance

https://mirror.codeforces.com/problemset/problem/9/D