<image>To ensure the secure transmission of information, there is a system called the Private Key Cryptosystem, with its encryption and decryption principles illustrated in the following diagram:

Now, the encryption key is y=2x-1, as shown: the plaintext "5" is encrypted to get the ciphertext "9", which is then sent. The recipient decrypts the ciphertext to get the plaintext "5" using the decryption key. If the recipient receives the ciphertext "17", what will the decrypted plaintext be? ____.