You are stranded in a land with only two big cities. Knightville is populated only by Knights, and Liarville - only by liars. Naturally, you wish to get to Knightville, where you hope to find help.

During your travels, you meet a resident of these parts, who must have come from one of the two cities, but you do not know which.

With one simple question, how do you find out what direction Knightville lies in?