def next(self):
    if (self.btn.text == 'Start'):
        self.lbl_sec.start()
        self.btn.text = 'Next'
    else:
        self.manager.transition.direction = 'left'
        self.manager.current = '4'
def next(self):
    if (self.btn.text == 'Start'):
        self.lbl_sec.start()
        self.btn.text = 'Next'
    else:
        self.manager.transition.direction = 'left'
        self.manager.current = '4'