Generate a program flowchart that will ask a user to input a test score. The loop will continue to ask the user to input the test scores until the user decides to stop. When the user decides not to enter any more scores, the program will calculate the average of all scores and print the letter grade. Based on the average score given below:

>=90 ------------------- A

>=80 and <90 --------- B

>=70 and <80 --------- C

>=60 and <70 --------- D

<60 --------------------- F