using System;
namespace CutDecimal
{
  public static class DecimalHelper
  {
    public static decimal CutDecimalWithN(decimal d, int n)
    {
      string strDecimal = d.ToString();
      int index = strDecimal.IndexOf(".");
      if (index == -1 || strDecimal.Length < index + n + 1)
      {
        strDecimal = string.Format("{0:F" + n + "}", d);
      }
      else
      {
        int length = index;
        if(n != 0)
        {
          length = index + n + 1;
        }
        strDecimal = strDecimal.Substring(0, length);
      }
      return Decimal.Parse(strDecimal);
    }
  }
}

static void Main(string[] args)
{
  decimal d = 1.23456789M;
  for (int i = 0; i <= 10; i++)
  {
    Console.WriteLine("{0}", DecimalHelper.CutDecimalWithN(d, i));
  }
  for (int i = 0; i <= 10; i++)
  {
    Console.WriteLine("{0}", Decimal.Round(d, i));
  }
}