'''Test if-elif-...-else determining a letter grade.'''

def letterGrade(score):
    if score >= 90:
        letter = 'A'
    elif score >= 80:
        letter = 'B'
    elif score >= 70:
        letter = 'C'
    elif score >= 60:
        letter = 'D'
    else:
        letter = 'F'
    return letter

def main():
    x = input('Enter a numerical grade: ')
    letter = letterGrade(x)
    print 'Your grade is %s.' % letter

main()