using System;

using System.Collections;

using System.Linq;

​

public static class Program

{

    public static void Main(string[] args)

    {

        var ht = new Hashtable

        {

            {23, 56000},

            {25, 67000},

            {26, 67000},

            {45, 54000}

        };

​

        var keysOrderedByValue = ht.Cast<DictionaryEntry>()

            .OrderBy(x => x.Value)

            .Select(x => x.Key);

​

        var result = string.Join(";", keysOrderedByValue);

​

        Console.WriteLine(result);

    }

}