input: from typing import Any
  
  def read_data_from_json(filename: str) -> Any:
      """Read data from a JSON file. Handle cases where the file does not exist or 
      is not in a valid JSON format.
      
      >>> read_data_from_json('nonexistent_file.json')
      "The file specified does not exist."
      
      >>> read_data_from_json('invalid_json_file.json')
      "The file specified is not in a valid JSON format."
      """
      try:
          with open(filename, 'r') as f:
              data = json.load(f)
          return data
      except FileNotFoundError:
          return "The file specified does not exist."
      except json.decoder.JSONDecodeError:
          return "The file specified is not in a valid JSON format."
output:     except json.decoder.JSONDecodeError:
          return "The file specified is not in a valid JSON format."