using System;

using System.Collections.Generic;

using System.Linq;                  

​

public class Program

{

    public static void Main()

    {

        List<decimal> list = new() { 23.346m, 23.56m, 4.2m, 0.90000000000000000000000000000m, 0.59333800m };

        List<decimal> sorted = new();

​

        foreach (var value in list)

        {

            sorted.Add(Numerics.GetValueAfterDecimalSeparator(value));

        }

​

        sorted.OrderByDescending(x => x).ToList().ForEach(x => Console.WriteLine(x));   

        Console.WriteLine();

        Console.WriteLine(sorted.OrderByDescending(x => x).FirstOrDefault());

    }

}

public class Numerics

{

    public static int GetValueAfterDecimalSeparator(decimal sender)

    {

        static decimal Normalize(decimal value)

            => value / 1.000_000_000_000_000_000_000_000_000_000_000m;

​

        decimal normalized = Normalize(sender); // remove trailing zeros

        int countDecimalNumbers = BitConverter.GetBytes(decimal.GetBits(normalized)[3])[2];

        decimal leftValue = Math.Floor(normalized);

        decimal rightValue = Math.Abs(leftValue - normalized);

        try

        {

            int multiplier = (int)Math.Pow(10, countDecimalNumbers);

            return decimal.ToInt32(decimal.Multiply(rightValue, multiplier));

        }

        catch (OverflowException)

        {

            return int.MaxValue;

        }

    }

}