using System;

using System.Collections;

​

public class Program

{

    public static void Main()

    {

        Hashtable ht = new Hashtable();

         ht.Add("001", "Shweta");

         ht.Add("002", "Ruchi");

         ht.Add("003", "Priya");

         ht.Add("004", "Meera");

         ht.Add("005", "Prachi");

         if (ht.ContainsValue("Riya")) {

            Console.WriteLine("This student name is already in the list");

         } else {

            ht.Add("006", "Riya");

         }

         // Get a collection of the keys.

         ICollection key = ht.Keys;

         foreach (string k in key) {

            Console.WriteLine(k + ": " + ht[k]);

         }

    }

   }

​