Five married couples gather for a party, 10 people total. One of them is a sociologist, and he desides to make a little research: at the end of the party he asks how many handshakes each of the participants made during the party. He gets 9 answers, all different, namely all integers from zero to eight. How many handshakes his wife made?


1. Nobody shakes hands with himself/herself or with his/her own spouse.

2. Each pair of people makes zero or one handshakes during the party.