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 result = new StringBuilder();

​

        //商數

        var quotient = num / 10;

​

        for (var i = 0; i < quotient; i++)

        {

            result.Append("0123456789");

        }

​

        //餘數，加1是因為循環第一位是0

        var remainder = num % 10 + 1;

​

        for (var i = 0; i < remainder; i++)

        {

            result.Append(i.ToString());

        }

​

        return result.ToString();

    }

}