/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left;
 *     public TreeNode right;
 *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
public class Solution {
    public int MaxDepth(TreeNode root) {
        if (root == null) return 0;
        int leftTree = MaxDepth(root.left) + 1;
        int rightTree = MaxDepth(root.right) + 1;
        return leftTree >= rightTree ? leftTree : rightTree; 
    }
}