OMCC 2021 Problem 4

There are $2021$ people at a meeting. It is known that one person at the meeting doesn't have any friends there and another person has only one friend there. In addition, it is true that, given any $4$ people, at least $2$ of them are friends. Show that there are $2018$ people at the meeting that are all friends with each other. *Note.*If $A$ is friend of $B$ then $B$ is a friend of $A$ .