exhaustion requirements of the PLRA “where a prisoner plaintiff plausibly seeks to counter defendants’ contention that the prisoner has failed to exhaust available administrative remedies as required by the PLRA.” Specifically, we instructed district courts to conduct a three-part inquiry to ascertain (1) whether administrative remedies were in fact “available” to the prisoner; (2) whether the defendants waived or are estopped from raising an affirmative defense of non-exhaustion of administrative remedies on account of their own actions inhibiting the prisoner from filing a grievance; and (3) whether there exist any alleged “special circumstances” that would excuse the prisoner’s failure to exhaust. Hemphill, 380 F.3d at 686; see, e.g., Giano v. Goord, 380 F.3d 670, 678 (2d Cir.2004) (<HOLDING>); Abney v. McGinnis, 380 F.3d 663 (2d Cir.2004)
holding that prisoner justifiably failed to file ordinary grievance when prisoner reasonably believed that department of corrections regulations foreclosed such recourse holding time begins when the prisoner knows  the important facts not when the prisoner recognizes their legal significance holding that a prisoner failed to exhaust his administrative remedies when he did not utilize grievance procedures that permitted waiver of the time limit for good cause holding remedies not available to prisoner where officials failed to respond to his grievance during time period required by regulations holding that a prisoner did not engage in protected conduct when he threatened to file a frivolous grievance