private void dataGridView1_MouseDown(object sender, MouseEventArgs e)
        {
            if (e.Button == MouseButtons.Right)
            {
                DataGridView.HitTestInfo hit = ((DataGridView)sender).HitTest(e.X, e.Y);
                if (hit.Type == DataGridViewHitTestType.Cell)
                {
                    DataGridViewCell clickedCell = ((DataGridView)sender).Rows[hit.RowIndex].Cells[hit.ColumnIndex];
                    ((DataGridView)sender).CurrentCell = clickedCell;
                }
            }
        }