private void Button_Click_1(object sender, RoutedEventArgs e)
{
StudentsWindow studentsWindow = new StudentsWindow(this, groups, students);
studentsWindow.Show();
Hide();
}
private void Button_Click_2(object sender, RoutedEventArgs e)
{
StudentsWindow studentsWindow = new StudentsWindow(mainWindow, groups, students);
studentsWindow.Show();
check = true;
Close();
}