using System;

using System.Collections.Generic;

using System.Linq;

​

public class Node {

    public int val;

    public IList<Node> children;

​

    public Node(){}

    public Node(int _val,IList<Node> _children) {

        val = _val;

        children = _children;

    }

​

}

public class Program

{

    public static void Main()

    {

        var tree = new Node() {

            val = 1,

            children = new List<Node>() {

                new Node() {

                    val = 3,

                    children = new List<Node>() {

                        new Node(){ val = 5 },

                        new Node(){ val = 6 }

                    }

                },

                new Node() {

                    val = 2

                },

                new Node() {

                    val = 4

                }

            }

        };

        var solution = new Solution();

        Console.WriteLine(solution.MaxDepth(tree));

        Console.WriteLine();

    }

}

​

public class Solution {

    public int MaxDepth(Node root) {

        if (root == null) {

            return 0;

        }

        var list = new List<int>() { 0 };

        if (root.children != null) {

            foreach (var item in root.children){

                list.Add(MaxDepth(item));

            }

        }

        return 1 + list.Max();

    }

}