Calculate Used Unit from Readings, C#

Calculate Used Unit from Readings

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            
            Int64 intCheckDigit = 5;
            decimal CurrentReding = 99242.00M;
            decimal LastReading = 102364.88M;

string strCheckDigitMaxNumber = "";
            for (int i = 1; i <= intCheckDigit; i++)
            {
                strCheckDigitMaxNumber += "9";
            }

string strInput = CurrentReding.ToString();
            try
            {
                strInput = strInput.TrimStart('0');
                if (strInput == "" || strInput == "0" || strInput == null)
                    strInput = "0.00";
            }
            catch { strInput = "0.00"; }
            int CurrentReding_Digit = Convert.ToInt64(Convert.ToDecimal(strInput)).ToString().Length;

strInput = LastReading.ToString();
            int LastDegit_Digit = Convert.ToInt64(Convert.ToDecimal(strInput.TrimStart('0'))).ToString().Length;

decimal decUsedUnit = 0;
            if (CurrentReding_Digit != LastDegit_Digit && CurrentReding < LastReading && LastDegit_Digit == intCheckDigit)
            {
                decimal decCheckDigitMaxNumber = Convert.ToInt64(strCheckDigitMaxNumber);
                decimal decMaxDigitRemainingReadingUnit = Convert.ToInt64(strCheckDigitMaxNumber) - LastReading;
                decUsedUnit = decMaxDigitRemainingReadingUnit + CurrentReding;
            }
            else
            {
                decUsedUnit = CurrentReding - LastReading;
            }
            Console.WriteLine(decUsedUnit);
        }
    }
}


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