#-*- 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)