Write a Python script that:

- prompts the user for a letter grade such as A, B-, C+, F

- converts the letter grade to a number GPA grade according to the the following rules:

(1) whole letters will convert to the numbers like so:

A = 4.0, B = 3.0, C = 2.0, D = 1.0, F = 0

(2) a '+' will add 0.3 to the GPA grade e.g. B+ = 3.3

a '-' will subtract 0.3 from the GPA grade e.g. B- = 2.7

(3) you can not have a GPA above 4.0 (A and A+ are both 4.0)

(4) F, F+ and F- are all equal to 0

- prints the number grade to the user