/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */


class Solution 
{
    public int maxDepth(TreeNode root)
    {
        if(root == null)
            return 0;

        int left = maxDepth(root.left);
        int right = maxDepth(root.right);

        return 1+ Math.max(left,right);
    }
}