python中出现'>=' not supported between instances of 'str' and 'int'错误

提示错误为： TypeError: '>=' not supported between instances of 'str' and 'int'
 因为 input 接收到的都是字符串类型，解决方案是转变字符类型。 
score=int(input ("请输入你的成绩:"))
if score >= 90:
    print('优秀')
elif score < 90 and score>=80:
    print('良好')
elif score < 80 and score>=60:
    print('及格')
else:
    print('不及格')