Agakhanov N.X.

At a round table, 30 people are sitting - knights and liars (knights always tell the truth, while liars always lie). It is known that each of them has exactly one friend at the same table, and a knight's friend is a liar, while a liar's friend is a knight (friendship is always mutual). When asked, "Is your friend sitting next to you?" every other person answered "Yes." How many of the rest could have also answered "Yes"?
All those sitting at the table are paired as friends, which means there are an equal number of knights and liars. Consider any pair of friends. If they are sitting next to each other, the knight will answer "Yes" to the given question, and the liar will answer "No." If they are not sitting next to each other, their answers will be opposite. In any case, exactly one of the pair of friends will answer "Yes." Therefore, all the other 15 answers will be "No."

## Answer

0.