The Leaf-Pruned K-th

Build a BST from a sequence of unique integers. A 'Pruning' operation removes all nodes that are currently leaves (nodes with no children). Perform one round of pruning, and then find the K-th smallest element in the remaining tree. If the tree becomes empty or has fewer than K nodes, output -1. Input Format: - Line 1: Space-separated integers for the BST. - Line 2: The integer K. Output Format: - The K-th smallest integer or -1. Example: Input: 10 5 15 2 7 12 18 2 Output: 10 Explanation: Initial leaves: 2, 7, 12, 18. Remaining nodes: 10, 5, 15. Sorted: 5, 10, 15. 2nd smallest is 10.