code: def find_files(folder):
      files = [i for i in os.listdir(folder) if i.startswith("left")]
      files.sort()
      for i in range(len(files)):
          insert_string = "right{}".format(files[i * 2][4:])
          files.insert(i * 2 + 1, insert_string)
      files = [os.path.join(folder, filename) for filename in files]
      return files