using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        SortedList<int, string> planets = new SortedList<int, string> {

            { 1, "Mercury" },

            { 2, "Venus" },

            { 3, "Earth" }

        };

         Console.WriteLine(planets.IndexOfKey(3)); //Returns 2

    }

}