9. Solve the following problem posed by Michael Khoury, U.S. Mathematics Olympiad Member, in “The Problem Solving Competition,” Oklahoma Publishing Company and the American Society for Communication of Mathematics, February 1999.

Bob is teaching a class with n students. There are n desks in the classroom, numbered from 1 to n. Bob has prepared a seating chart, but the students have already seated themselves randomly. Bob calls off the name of the person who belongs in seat 1. This person vacates the seat he or she is currently occupying and takes his or her rightful seat. If this displaces a person already in the seat, that person stands at the front of the room until he or she is assigned a seat. Bob does this for each seat in turn. After k (1 ≤ k < n) names have been called, what is the expected number of students standing at the front of the room?