Grade Reporter

Write a main program that takes a grade percentage as input (ordinarily 0 - 100), and then sends that information via a parameter to a function called evaluate_grade(). That function should return a string value of A, B, C, D, or F, depending on the value of the parameter.

Values higher than 100 are acceptable, values lower than 0 are not. The evaluate_grade function should return the Python value None for the case of negative values.

Test cases:

Input --> Output
 100        A
  99        A
  90        A
  82        B
  75        C
  64        D
  59        F
 105        A
  -1        None