using System;

using System.Collections.Generic;           

public class Program

{

​

    public static void Main()

    {

        var dict = new Dictionary<string, object>();        

        dict.Add("first", new object());

        dict.Add("second", new object());

        dict.Remove("first");

        dict.Add("third", new object());

​

        foreach (var entry in dict)

        {

            Console.WriteLine(entry.Key);

        }

    }

}