print ('Please enter your four test grades in the prompts below.')
testAverage = 0

while testAverage != -1:
    test1 = int(input('Please enter your first test grade: '))
    test2 = int(input('Please enter your second test grade: '))
    test3 = int(input('Please enter your third test grade: '))
    test4 = int(input('Please enter your fourth test grade: '))
    testAverage = (test1+test2+test3+test4)/4

    if testAverage >=90:
        print ('You have an A in the class, your test average is: ', testAverage)
    if 80 <= testAverage < 90:
        print ('You have a B in the class, your test average is: ', testAverage)
    if 70 <= testAverage < 80:
        print ('You have a C in the class, your test average is: ', testAverage)
    if 60 <= testAverage < 70:
        print ('You have a D in the class, your test average is: ', testAverage)
    if testAverage >= 70:
        print ('You have passed this course.')
else:
    print ('You have received an F and have failed this course.')