using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var planets = new Dictionary<int, string>()

        {

            [1] = "Mercury",

            [2] = "Venus",

            [3] = "Earth"

        };

​

         Console.WriteLine("-----Loop 1-----");

        foreach (var key in planets.Keys)

            Console.WriteLine(key);

        // Copy all the keys and than iterate

        Dictionary<int, string>.KeyCollection keys = planets.Keys;

        Console.WriteLine("-----Loop 2-----");

        foreach (var key in keys)

            Console.WriteLine(key);

​

    }

}