private void Navigate_back(object sender, RoutedEventArgs e)
 {
     if (FraMain.CanGoBack)
     {
         FraMain.GoBack();
     }
 }
 private void Button_Click(object sender, RoutedEventArgs e)
 {
     FraMain.Navigate(new Page4_book_service());
 }
 private void Server_list(object sender, RoutedEventArgs e)
 {
     FraMain.Navigate(new Page_3());//search_list
 }
 private void Client_LIst(object sender, RoutedEventArgs e)
 {
     FraMain.Navigate(new Page2());///Client-page
 }
 public MainWindow()
 {
     InitializeComponent();
     FraMain.Navigate(new Page_1());//страница приветстви
 }