How to Close Application From Child Form Rather Than Parent Form in WPF

Hello,

I am using a Login Page as my startup page. After Login MainWindow.xaml is showing and Login Page is hiding. I want to Exit all application on Exit Button of MainWindow form.

I am trying to close but unable to close it... Anyone can help me in this regard ??

I am using XAML form Based Application...

Thanks

Jazaib Hussain