using System;

public class Program

{

    public static void Main()

    {

Console.WriteLine(AddDecimals(10.00M,2));   

        Console.WriteLine(AddDecimals(10.50M,2));   

        Console.WriteLine(AddDecimals(10.51M,2));   

        Console.WriteLine(AddDecimals(10.519M,2));  

        Console.WriteLine(AddDecimals(10.90M,2));   

        Console.WriteLine(AddDecimals(10,2));   

    }

    public static string AddDecimals(decimal? value, int decimalCount = 2)

        {

            string returnValue = "0.00";

            if ((value??0) > 0) {

                string format = $"{{0:0.{0.ToString().PadRight(decimalCount,'0')}}}";

                returnValue = String.Format(format, value);

            }

            return returnValue;

        }

}