Except as otherwise provided in this section, a person who violates a provision of §§ 5–602 through 5–606 of this subtitle with respect to a Schedule I or Schedule II narcotic drug is guilty of a felony and on conviction is subject to imprisonment not exceeding 20 years or a fine not exceeding $15,000 or both. A person who is convicted under subsection (a) of this section or of conspiracy to commit a crime included in subsection (a) of this section is subject to imprisonment not exceeding 20 years or a fine not exceeding $15,000 or both if the person previously has been convicted once: under subsection (a) of this section or § 5–609 of this subtitle; of conspiracy to commit a crime included in subsection (a) of this section or § 5–609 of this subtitle; or of a crime under the laws of another state or the United States that would be a crime included in subsection (a) of this section or § 5–609 of this subtitle if committed in this State. A person who is convicted under subsection (a) of this section or of conspiracy to commit a crime included in subsection (a) of this section is subject to imprisonment not exceeding 25 years or a fine not exceeding $25,000 or both if the person previously: has served at least one term of confinement of at least 180 days in a correctional institution as a result of a conviction: under subsection (a) of this section or § 5–609 or § 5–614 of this subtitle; of conspiracy to commit a crime included in subsection (a) of this section or § 5–609 of this subtitle; or of a crime under the laws of another state or the United States that would be a crime included in subsection (a) of this section or § 5–609 of this subtitle if committed in this State; and has been convicted twice, if the convictions arise from separate occasions: under subsection (a) of this section or § 5–609 of this subtitle; of conspiracy to commit a crime included in subsection (a) of this section or § 5–609 of this subtitle; of a crime under the laws of another state or the United States that would be a crime included in subsection (a) of this section or § 5–609 of this subtitle if committed in this State; or of any combination of these crimes. A separate occasion is one in which the second or succeeding crime is committed after there has been a charging document filed for the preceding crime. A person who is convicted under subsection (a) of this section or of conspiracy to commit a crime included in subsection (a) of this section is subject to imprisonment not exceeding 40 years or a fine not exceeding $25,000 or both if the person previously has served three or more separate terms of confinement as a result of three or more separate convictions: under subsection (a) of this section or § 5–609 of this subtitle; of conspiracy to commit a crime included in subsection (a) of this section or § 5–609 of this subtitle; of a crime under the laws of another state or the United States that would be a crime included in subsection (a) of this section or § 5–609 of this subtitle if committed in this State; or of any combination of these crimes. A person convicted under subsection (a) of this section or of conspiracy to commit a crime included in subsection (a) of this section is not prohibited from participating in a drug treatment program under § 8–507 of the Health – General Article because of the length of the sentence.