using System;

using System.Text;

​

public class Program

{

    public static void Main()

    {

        var builder = new StringBuilder();

        builder.AppendLine("One,");

        builder.Length--; // Won't work

        Console.WriteLine(builder.ToString());

        builder = new StringBuilder();

        builder.AppendLine("One,");

        builder.Length += -1; // Won't work

        Console.WriteLine(builder.ToString());

        builder = new StringBuilder();

        builder.AppendLine("One,");

        Console.WriteLine(builder.ToString().TrimEnd(',')); // Won't work

    }

}