using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var elNum = new Stack<int>();

        elNum.Push(100);

        elNum.Push(200);

        elNum.Push(300);

        elNum.Push(400);

​

        Console.WriteLine(elNum.Contains(300));  // True

        Console.WriteLine(elNum.Contains(150));  // False

    }

}