Why Kivymd MDSwiper is occuring unknown class error?

I am new to kivymd and I was testing with MDSwiper.
But when I run my code, It occurs some errors.
I think I’m making some stupid mistakes but i don’t know how to solve this problem.

my code:

from kivymd.app import MDApp
from kivy.lang.builder import Builder

KVstring = """
Screen:
    MDSwiper:
        MDSwiperItem:
            MDLabel:
                halign: "center"    
                text: "Hello MDswiper"
        MDSwiperItem:
            MDLabel:
                halign: "center"    
                text: "I hate Errors"
"""

class MainApp(MDApp):
    def build(self):
        screen1 = Builder.load_string(KVstring)
        return screen1

MainApp().run()

my error message:

kivy.factory.FactoryException: Unknown class <MDSwiper>

Thanks.