Find K-th Smallest Element in BST

You are given the root node of a binary search tree (BST) and an integer k. Your task is to find the k-th smallest element in the BST. The smallest element is considered to be the first one. If k exceeds the number of nodes in the tree, return -1. Input format: - The first line contains an integer n, the number of nodes in the BST. - The following n lines contain three integers each: the first integer is the node value, and the next two integers are the indices of the left and right children (or -1 if no child). - The last line contains an integer k. Output format: - Print the k-th smallest element or -1 if it does not exist. Example: Input: 3 5 1 2 3 -1 -1 7 -1 -1 2 Output: 5