#!/usr/bin/env python
#
# Author  : Ahmed Obied (amaobied@ucalgary.ca)
# Date    : Jan. 17th 2008
# Purpose : Calculates the percentage and letter grade based on a given
#           total and mark
# 

# boolean to control the loop
end_loop = False
while not end_loop:

    # get the total and make sure it's greater than zero
    total_marks = float(raw_input('Enter the total number of marks: '))
    if total_marks <= 0:
        print 'Error: The number must be greater than zero.'
    else:

        # if we get a number greater than zero then we stop iterating
        end_loop = True

end_loop = False
while not end_loop:

    # get the mark and make sure it's greater than zero
    mark = float(raw_input('Enter your mark : '))

    # check if the mark is in the proper range
    if mark < 0 or mark > total_marks:
        print 'Error: incorrect input'
    else:
        end_loop = True

# calculate the percentage value 
percentage = (mark * 100.0) / total_marks

# find the letter grade based on the computed percentage 
if percentage < 39.0:
    letter_grade, letter_sign = 'F', ' '
elif percentage < 44.0:
    letter_grade, letter_sign = 'D', '-'
elif percentage < 49.0:
    letter_grade, letter_sign = 'D', ' '
elif percentage < 54.0:
    letter_grade, letter_sign = 'D', '+'
elif percentage < 59.9:
    letter_grade, letter_sign = 'C', '-'
elif percentage < 64.0:
    letter_grade, letter_sign = 'C', ' '
elif percentage < 69.0:
    letter_grade, letter_sign = 'C', '+'
elif percentage < 74.0:
    letter_grade, letter_sign = 'B', '-'
elif percentage < 79.0:
    letter_grade, letter_sign = 'B', ' '
elif percentage < 84.0:
    letter_grade, letter_sign = 'B', '+'
elif percentage < 89.0:
    letter_grade, letter_sign = 'A', '-'
else:
    letter_grade, letter_sign = 'A', ' '

# write the output to the console with proper formatting
print 'You got %.2f%c on the test which gives you a letter grade of %c%c' % \
      (percentage, '%', letter_grade, letter_sign)