using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Linq;
public class Test
{
	public static void Main()
	{
		var line = "a, s, f, double, double, 12, sd, 1";
		var latIndex = 5;
		var pat = $@"^((?:[^,]*,){{{latIndex+1}}})(.*)";
		Console.WriteLine(pat);
		var veiRef = "str";
		line = Regex.Replace(line, pat, $"${{1}}{veiRef.Replace("$","$$")}$2");
		Console.WriteLine(line);
	}
	
	
}