#-*- coding: UTF-8 -*-
# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def maxDepth(self, root):
        if root==None:return 0
        leftDepth=self.maxDepth(root.left)
        rightDepth=self.maxDepth(root.right)
        
        return leftDepth+1 if leftDepth >rightDepth else (rightDepth+1)