Some people know each other in a group of people, where "knowing" is a symmetric relation. For a person, we say that it is social if it knows at least 20 other persons and at least 2 of those 20 know each other. For a person, we say that it is shy if it doesn't know at least 20 other persons and at least 2 of those 20 don't know each other. Find the maximal number of people in that group, if we know that group doesn't have any social nor shy persons. JBMO TSTcombinatoricsnational olympiad