using System;

public class Program

{

    LLNode root = null;

    static int count = 0;  

    public void Main()

    {

            PushLL(1);

            PushLL(2);

            PushLL(3);

            PushLL(4);

            PushLL(5);

            var node = root;

            PopLL();

            var node1 = root;

            PopLL(3);

            var node2 = root;

            PopLL(2);

            var node3 = root;

            PopLL(4);

            var node4 = root;

    }

    private LLNode PopLL(int? number = null)

        {

            LLNode pointer1 = root;

            LLNode pointer2 = root;

            LLNode head = pointer1;

            if (count > 0)

            {

                while (pointer1 != null)

                {

                    if (number != null)

                    {

                        if (number == pointer1.Value)

                        {

                            LLNode temp = pointer1;

                            temp = null;

                            pointer2.Next = pointer1.Next;

                            pointer1 = pointer1.Next;

                            count--;

                        }

                        else

                        {

                            pointer2 = pointer1;

                            pointer1 = pointer1.Next;

                        }

                    }

                    else//removing first node by default if input param is null

                    {

                        root = pointer1.Next;

                        count--;    

                        return root;

                    }

                }

            }

            return head;

        }

​

    private void PushLL(int number)

        {

            LLNode node = new LLNode();

            node.Value = number;

​

            if (root == null)

                root = node;

            else

            {

                node.Next = root;

                root = node;

            }

            count++;                      

        }

}

public class LLNode

    {

        public int Value { get; set; }

        public LLNode Next { get; set; }

    }