my kivy simple hello world app is not closing I'm using raspberry pi B and I can't close it I must unplug my raspberry pi 5v adapter to close it

I'm using rasbian jessie this is the very simple code

import kivy
from kivy.app import App
from kivy.uix.label import Label

class mamdouh(App):
    def build(self):
        retu Label(text='mamdouh')

if __name__=='__main__':
    mamdouh().run()