The Borrowed Camel

A herder dies and leaves his seventeen camels to his three sons. His instructions say that the eldest must receive one half of the herd, the middle son one third, and the youngest one ninth. The camels cannot be sold, killed, or divided, and the sons must follow the stated fractions exactly. Since seventeen does not divide evenly by any of those fractions, the brothers ask a wise neighbour for help. She temporarily adds one of her own camels to the herd, distributes the inheritance without splitting a single animal, and then takes her camel home again. How many camels does the eldest son receive?