A 58-year-old man from Delhi presents to the emergency department with acute onset left hemiparesis and left facial droop. On examination, he has left-sided weakness (3/5) with hyperreflexia and an extensor plantar response. CT brain shows no hemorrhage. CT angiography reveals complete occlusion of the right middle cerebral artery (MCA) at its origin. On further imaging, a hypoplastic right anterior cerebral artery (ACA) is noted. Which vessel of the Circle of Willis is most likely compensating for the blood supply to the right ACA territory?