input: def encrypt_decrypt_string(plaintext: str) -> str:
      """ Encrypts the given plaintext using AES encryption and then decrypts it back.
      Returns the decrypted text.
      >>> encrypt_decrypt_string('Hello World')
      'Hello World'
      >>> encrypt_decrypt_string('Secret Message')
      'Secret Message'
      """
      from Crypto.Cipher import AES
      key = b'Sixteen byte key'
      
      def encrypt(text: str) -> bytes:
          cipher = AES.new(key, AES.MODE_ECB)
          return cipher.encrypt(text.encode())
      
      def decrypt(ciphertext: bytes) -> str:
          cipher = AES.new(key, AES.MODE_ECB)
          return cipher.decrypt(ciphertext).decode()
      
      encrypted_text = encrypt(plaintext)
      decrypted_text = decrypt(encrypted_text)
      return decrypted_text
output:     padded_plaintext = plaintext + (16 - len(plaintext) % 16) * chr(16 - len(plaintext) % 16)
      encrypted_text = encrypt(padded_plaintext)
      decrypted_text = decrypt(encrypted_text)
      return decrypted_text[:-ord(decrypted_text[-1])]