using System;

public class Program

{

    public static void Main()

    {

        var input = "There, are an awful, awfully, large amount of commas in this, sentence, many are wrong.";

        Console.WriteLine(RemoveAllButFirst(input,","));

    }

    public static string RemoveAllButFirst(string s, string stuffToRemove)

    {

        // Check if the stuff to replace exists and if not, return the original string

        var locationOfStuff = s.IndexOf(stuffToRemove);

        if (locationOfStuff < 0)

        {

            return s;

        }

        // Calculate where to pull the first string from and then replace the rest of the string

        var splitLocation = locationOfStuff + stuffToRemove.Length;

        return s.Substring(0, splitLocation) +  (s.Substring(splitLocation)).Replace(stuffToRemove,"");

    }

}