The mandatory period of parole supervision imposed under NERA is part of a unitary sentence that is penal in nature. The State has kept Njango in prison for more than a year beyond his release date. Without credit for the excess prison time, Njango would serve more time in the custody of the Department of Corrections than authorized by his sentence. Under the fundamental fairness doctrine -- an integral part of the due process guarantee of the New Jersey Constitution -- the excess time Njango erroneously served in prison must be credited to reduce the period of his parole supervision.