How to modify the existing code to output an average of -1, if the user enters -1 at the start?

Task: Modify the StudentGradesDoWhile.java program so that when the user enters -1 as the first value, you get an average of -1.

While still running normally when this case was not added. i.e. -1 stops the program from running after values are given.

Given program for StudentGradesDoWhile.java