Replace the question mark with a number

Donald MacDonald from Scotland went to study at an English university and was living in the hall of residence with all the other students there. After he had been there a month, his mother came to visit him (no doubt carrying reinforcements of tatties, salt herring, oatmeal and whisky).

“And how do you find the English students, Donald?” she asked.

“Mother,” he replied, “they're such terrible, noisy people. The one on that side keeps banging his head on the wall and won't stop. The one on the other side screams and screams all night.”

“Oh Donald! How do you manage to put up with these awful noisy English neighbors?”

“Mother, I do nothing. I just ignore them. I just stay here quietly, playing my bagpipes.”