If there is 1 person tell truth, it will be right. Because the other wil say that, 1 people tell the truth is among of each person's neighbors,exepct the person tell the truth. But if 2 or more, it will be wrong. Because there are 13 neighbors, if there are 2 or more tell the truth, number people tell the truth is increase among of each person neighbors.
So there are 13 people are liars.