MathDB

6

Part of 2016 Japan TST

Problems(1)

IMO fever

Source: 2016 Japan TST P6

1/26/2023
There are 20152015 people. Initially, only one of these people is infected with IMO fever, but we don't know who it is. When two people shake hands, if one of them is infected with IMO fever, the other person get infected with it. Determine the minimum number of handshakes needed to infect all 20152015 people, regardless of who the first infected person is.
combinatorics