Start your code with three comment lines explaining the program purpose, your name and the date have written. You MUST submit your own work using the concepts taught in the class, only. (Otherwise, you will get a zero mark.) Write a program to validate a username. The program asks the user to his/her username. Suppose, the correct name of the user is "Sara Johnson".

1. If the username is entered correctly, then the program prints a greeting message to welcome the user: Welcome Sara Johnson!
2. If the user enters an incorrect username (suppose, Michael Johnson), then the program displays a message: Michael Johnson is an invalid username. Try again!
3. Allow four chances for the user to enter a correct username.

Hint: Use a while loop. See lecture slides for a similar problem.