using System;

public class Program

{

    public static void Main()

    {

        var dec = Decimal.Parse( "3178.71121299267689");

                                //3178.71121299267689

                                //3178.7112129926772    

        var doub1 = (double)dec;

        var doub2 = Decimal.ToDouble(dec);

        var dec2 = Math.Round(dec, 13, MidpointRounding.ToEven);

        Console.WriteLine("dec=   " + dec);

        Console.WriteLine("doub1= " + doub1);

        Console.WriteLine("doub2= " + doub2);

        Console.WriteLine("dec2=  " + dec2);

    }

}