using System;

using System.Text.RegularExpressions;

public class Program

{

    static string Seprator(Match m)

 {

     return int.Parse(m.ToString()).ToString("N0");

 }

    public static void Main()

    {

        string a = "1234km";

            string result =  Regex.Replace(a, "\\d+",new MatchEvaluator(Seprator));

        Console.WriteLine(result);

    }

}