using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TodoApplication
{
    public class Item<T>
    {
        public T Value { get; set; }
        public Item<T> Previous { get; set; }
        public Item<T> Next { get; set; }
    }

    public class LimitedSizeStack<T>
    {
        public int Limit;
        public int CountVar;
        public Item<T> Start = new Item<T> { Previous = null, Next = null };
        public Item<T> Final = new Item<T> { Previous = null, Next = null };

        public LimitedSizeStack(int limit)
        {
            Limit = limit;
        }

        public void Push(T item)
        {
            if (Start != null)
            {
                if (CountVar < Limit)
                {
                    CountVar++;
                    Final.Next = new Item<T> { Value = item, Previous = Final };
                    Final = Final.Next;
                }
                else if (CountVar == Limit)
                {
                    Final.Next = new Item<T> { Value = item, Previous = Final };
                    Final = Final.Next;

                    Start = Start.Next;
                    Start.Previous = null;
                }
            }
            else
            {
                CountVar++;
                Start = Final = new Item<T> { Value = item };
            }
        }

        public T Pop()
        {
            if (Start != Final)
            {
                var value = Final.Value;
                Final = Final.Previous;
                Final.Next = null;
                CountVar--;
                return value;
            }
            else
            {
                var value = Start.Value;
                Start = Final = null;
                CountVar--;
                return value;
            }
        }

        public int Count
        {
            get
            {
                return CountVar;
            }
        }
    }
}