Find Node Depth in a Binary Tree

You are given a binary tree and an integer target value. Your task is to determine the depth of the node that contains the target value. The depth of a node is defined as the number of edges from the root node to that node. Formally, for a node with depth \( d \), the root has depth \( 0 \) and any child node has depth \( d+1 \).

If the target value does not exist in the tree, output \(-1\).

The binary tree is provided in level order where the value null indicates a missing node. The first line of input contains the level-order traversal of the tree (node values separated by spaces), and the second line contains the target integer.

Example:

Input:
3 9 20 null null 15 7
15
Output:
2

</p>

inputFormat

The input consists of two lines:

1. The first line contains the level order traversal of the binary tree. Node values are separated by a space. Use null to denote a missing node.
2. The second line contains a single integer representing the target value whose depth is to be found.

Note that the tree could be empty; in such a case, the first token will be null.

outputFormat

Output a single integer which is the depth of the node containing the target value. If the target value does not exist in the tree, output -1.

## sample

3 9 20 null null 15 7
15

2