private void Button_Click_NextGrid(object sender, RoutedEventArgs e)
        {
            Count_Grid_Subject += 5;
            subjects_grid d = new subjects_grid();

            d.Show();
            this.Close();
        }
        private void Button_Click_PreviousGrid(object sender, RoutedEventArgs e)
        {
            Count_Grid_Subject -= 5;
            if (Count_Grid_Subject == 0)
            {
                Count_Grid_Subject = 5;
            }
            subjects_grid d = new subjects_grid();

            d.Show();
            this.Close();
        }