using System;

using System.Text;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(GetNumString(6));

        Console.WriteLine(GetNumString(15));

        Console.WriteLine(GetNumString(23));

    }

    public static string GetNumString(int num)

    {

        var template = "0123456789";

​

        var result = new StringBuilder();

        for (var i = 0; i < num / template.Length; i++)

        {

            result.Append(template);

        }

        result.Append(template.Substring(0, num % template.Length + 1));

​

        return result.ToString();

    }

}