import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @return int整型
     */

    
    public int maxDepth (TreeNode root) {
        if(root==null){
            return 0;
        }
        int line=0;
        if(root!=null){
            line++;
        }
        int leftH=maxDepth(root.left);
        
        int rightH=maxDepth(root.right);

        return Math.max(leftH,rightH)+1;
        

         
    }
   










}