using System;

public class Program

{

    public static void Main()

    {

        string s = "000010123";

​

        string result = FormatServiceNumber(s);

​

        Console.WriteLine(result); //010123

    }

    // Complexity O(n)

    public static string FormatServiceNumber(string serviceNumber) // No single letter method parameters

    {        

         var newServiceNumber = serviceNumber.TrimStart(BillIngestionConstants.ZeroPrefix);

         return $"{BillIngestionConstants.ZeroPrefix}{newServiceNumber}";

    }

    public static class BillIngestionConstants

    {

        public const char ZeroPrefix = '0'; // Changed to char

    }

}