C# rename files

static void RenameFiles()
        {
            string sourceDir = @"D:\ll";
            string[] allFiles = Directory.GetFiles(sourceDir, "*.mp3", SearchOption.AllDirectories);

            if(allFiles!=null && allFiles.Any())
            {
                for(int i = ; i < allFiles.Count(); i++)
                {
                    string newName =Path.Combine(sourceDir, i + ".mp3");
                    File.Move(allFiles[i], newName);
                }
            }
        }