using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var queue = new ConcurrentQueue<int>();

        queue.Enqueue(5);

        queue.Enqueue(7);

        Console.WriteLine(queue.Average());

    }

}

​

public static class ExtensionMethodsForQueue {

     public static double Average(this ConcurrentQueue<int> queue) 

     {

             return queue.CopyToArray().Average();

     }

}

​

public class ConcurrentQueue<T>{

        private readonly object syncLock = new object();

        private Queue<T> queue;

​

        public int Count

        {

            get

            {

                lock(syncLock) 

                {

                    return queue.Count;

                }

            }

        }

​

        public ConcurrentQueue()

        {

            this.queue = new Queue<T>();

        }

​

        public T Peek()

        {

            lock(syncLock)

            {

                return queue.Peek();

            }

        }   

​

        public void Enqueue(T obj)

        {

            lock(syncLock)

            {

                queue.Enqueue(obj);

            }

        }

​

        public T Dequeue()

        {

            lock(syncLock)

            {

                return queue.Dequeue();

            }

        }

​

        public void Clear()

        {

            lock(syncLock)

            {

                queue.Clear();

            }

        }

​

        public T[] CopyToArray()

        {

            lock(syncLock)

            {

                if(queue.Count == 0)

                {

                    return new T[0];

                }

​

                    T[] values = new T[queue.Count];

                queue.CopyTo(values, 0);    

                return values;

            }

        }

​

        public static ConcurrentQueue<T> InitFromArray(IEnumerable<T> initValues)

        {

            var queue = new ConcurrentQueue<T>();

​

            if(initValues == null)  

            {

                return queue;

            }

​

            foreach(T val in initValues)

            {

                queue.Enqueue(val);

            }

​

            return queue;

        }

    }