using System;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

​

​

    public class RecentlyUsedList<T> : IList<T>

    {

        private List<T> items = new List<T>(); 

​

        public IEnumerator<T> GetEnumerator()

        {

            return items.GetEnumerator();

        }

​

        public override bool Equals(object obj)

        {

            return base.Equals(obj);

        }

​

        IEnumerator IEnumerable.GetEnumerator()

        {

            return GetEnumerator();

        }

​

        public void Add(T item)

        {

            if (items.Contains(item))

            {

                items.Remove(item);

            }

            items.Insert(0, item);

        }

​

        public void Clear()

        {

            items.Clear();

        }

​

        public bool Contains(T item)

        {

            return items.Contains(item);

        }

​

        public void CopyTo(T[] array, int arrayIndex)

        {

            items.CopyTo(array, arrayIndex);

        }

​

        public bool Remove(T item)

        {

            return items.Remove(item);

        }

​

        public int Count

        {

            get { return items.Count; }

        }

​

        public bool IsReadOnly { get; private set; }

        public int IndexOf(T item)

        {

            return items.IndexOf(item);

        }

​

        public void Insert(int index, T item)

        {

            throw new NotSupportedException();

        }

​

        public void RemoveAt(int index)

        {

            items.RemoveAt(index);

        }

​

        public T this[int index]

        {

            get { return items[index]; }

            set { items[index] = value; }

        }

    }