"""
Google interview question

Given a list of employees and who reports to those employees, e.g.

1: [2, 3]
2: [4, 5]
3: []
4: []
5: []

Write a function which returns the total number of reporting employees, given an employee number. An employee counts as
reporting to him/herself. Should return -1 in cases where the data is invalid in any way.
"""