"""
# Definition for a Node.
class Node:
def __init__(self, val, children):
self.val = val
self.children = children
"""
class Solution:
def maxDepth(self, root: 'Node') -> int:
if root is None:
return 0
elif not root.children:
return 1
else:
return 1 + max(self.maxDepth(node) for node in root.children)