如何在应用程序中释放主视图控制器(First视图控制器)中的内存?

While we returning back to the 2nd view controller to main view controller, The Dealloc method is called and all the allocated memory is released of that view controller that is 2nd view controller. Then when will the dealloc method is called of Master View Controller that is First view contoller.While we returning back to the 2nd view control