HawkSearch field naming convention, C#

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

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine(GetStandardFieldName("Hello, world!")); 
            Console.WriteLine(GetStandardFieldName("99Hello, world!")); 
            Console.WriteLine(GetStandardFieldName("_1Hello, world!_"));
        }
        
        public static string GetStandardFieldName(string InputField)
        {
            var rgx = new System.Text.RegularExpressions.Regex("[^a-zA-Z0-9_]");

string SField = InputField;
            SField = SField.Replace(" ", "_");
            SField = rgx.Replace(SField, "");

if (!string.IsNullOrEmpty(SField))
            {
                SField = SField.ToLower();
                if (SField.StartsWith("_"))
                    SField = SField.Remove(0, 1);
                if (SField.EndsWith("_"))
                    SField = SField.Remove(SField.Length - 1);
            }

if (!string.IsNullOrEmpty(SField))
            {
                if(int.TryParse(SField.Substring(0, 1), out int result))
                    SField= "n" + SField;
            }

return SField;
        }
    }
}

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Compilation time: 1.44 sec, absolute running time: 0.42 sec, cpu time: 0.29 sec, memory peak: 41 Mb, absolute service time: 2,03 sec