def percentToGrade(percent):
    """takes a percentage and outputs the letter grade"""

    if percent >= 85:
        return "A"
    elif percent >= 75:
        return "B"
    elif percent >= 65:
        return "C"
    elif percent >= 55:
        return "D"
    else:
        return "F"
    


percent = float(raw_input("Enter the percentage grade: "))
print "The student earned a(n) " + percentToGrade(percent) + "."