Final Grade Calculator Python

constant = 1
firstrun = True
def intro():
    print ""
    print "this program will tell you what grade you can"
    print "get on the final and still keep a certian letter grade."
    print ""

def inter():
    print ""
    print "Do you want to calculate your grade again. (y,n)"

def start():
    print ""
    print "What grade do you have in the class"

    grade = input( ">" ) # Getting the input of the grade
    grade2 = grade*0.8   # The final is worth 20% of your grade, thus the .8

    # The if else function here will tell you what score you can get on the final and
    # keep an A in the class. If the result is zero,
    # then you will get AT LEAST that grade
    print "For an A"
    if (89.55-grade2)/20<0:
        print ( "0" )
    else: print (((89.55-grade2)/20)*100)

    print "for a B"
    if (79.55-grade2)/20<0:
        print ( "0" )
    else: print (((79.55-grade2)/20)*100)

    print "for a C"
    if (69.55-grade2)/20<0:
        print ( "0" )
    else: print (((69.55-grade2)/20)*100)

    print "for a D"
    if (59.55-grade2)/20<0:
        print ( "0" )
    else: print (((59.55-grade2)/20)*100)
    print "NOTE- if there is a 0 or a number over 100 displayed on the grade,"
    print "that means that you can not get that grade"




while constant == 1:
    if firstrun == True:
        intro()
        start()
        firstrun = False # sets the variable to false so it will go to the else on the next run
        inter()
        # I was having some trouble with the repeting scrips not asking if you wanted
        # to calculate the grade again and would just give you a promp for it. so I added
        # another function that did ask

    else:
        answer = raw_input ( ">" ) # dont forget to add a raw_input, it can be very frusterating when you dont.
        if answer == "y":
            start()
            print ""
            print "Do you want to calculate your grade again.(y,n)"

        else:
            exit()