input: from Crypto.Cipher import AES
  
  key = b'Sixteen byte key'
  
  def encrypt_decrypt_app(plaintext: bytes) -> bytes:
      """ This function encrypts the given plaintext using the AES algorithm in ECB mode.
      It then decrypts the encrypted text back to the original plaintext.
      The key for encryption and decryption is a constant 'Sixteen byte key'.
      Returns the decrypted plaintext.
      
      >>> encrypt_decrypt_app(b'Hello World!')
      b'Hello World!'
      >>> encrypt_decrypt_app(b'Encryption is fun!')
      b'Encryption is fun!'
      """
      cipher = AES.new(key, AES.MODE_ECB)
      encrypted_text = cipher.encrypt(plaintext)
      decrypted_text = cipher.decrypt(encrypted_text)
      return decrypted_text
output:     cipher = AES.new(key, AES.MODE_ECB)
      encrypted_text = cipher.encrypt(plaintext)
      decrypted_text = cipher.decrypt(encrypted_text)
      return decrypted_text