Is it possible to get Silverlight's first load event (ie.check condition depends on first load event)

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Silverlight

Suppose,
I have three pages in project.(mainpage,loginin,third)
when i start the project, mainpage opens(mainpage.xmal)

i want to make both two pages starts(mainpage,login)
so i make like this,

void MainPage_Loaded(object sender, RoutedEventArgs e)
       {
           App app = (App)Application.Current;
           App.Navigate(new Login());
        }

It is Ok to start both main page and login page.

But,in third page(xxxxxx.xmal)
I have to call main page and NextPage

public void Link_Click(object sender, RoutedEventArgs e)
        { 
                    App.Navigate(new MainPage());
                    App.Navigate(new NextPage());
           }

Now, that is the problem that MainPage call Login Page .That time is not OK to call Login Page.
Described In my question,

is it possible to make check condition depends on first load event?
eg
if (silverlight project first time load)
{
//OK
}

Or
How can i make show two pages at initial and than call main page only again
Thanks for any suggestions or advice.