定义一个赋值0-100的整数，并将百分制成绩转化成五级成绩输出

score_number = int(input('请输入你的成绩：'))
if 90 <= score_number <= 100:
    print('优秀')
elif 80 <= score_number <= 89:
    print('良好')
elif 70 <= score_number <= 79:
    print('中等')
elif 60 <= score_number <= 69:
    print('及格')
elif 0 <= score_number <= 59:
    print('不及格')
else:
    print('无效成绩')