Inventory Shelf Depth

In a smart library, books are indexed in a BST by their unique serial number. The 'depth' of a book determines which shelf height it is on (the root is at depth 0, its children at depth 1, etc.). Given a sequence of serial numbers to build a BST and a target serial number, find the depth of that target. If the serial number is not in the tree, output -1. Input Format: Line 1: Space-separated integers representing the serial numbers in insertion order. Line 2: A single integer representing the target serial number. Output Format: An integer representing the depth, or -1 if not found. Example: Input: 50 30 70 20 40 60 80 60 Output: 2