Problem when summing datagridview selected cells

Question

Hi guys

I to label (tlblPriceTotal) show sum of all selected cells.

I programed this code

But it does not works correctly. when i selecte something this code begin summing from first row

if i select another column it summing same (priceDataGridViewTextBoxColumn)

what is problem can anybody help me?

Thanks.

 private void dataGridView1_SelectionChanged(object sender, EventArgs e)
    {
      decimal nextNumber = 0;
      decimal sumNumbers = 0;

      for (int i = 0; i < dataGridView1.SelectedCells.Count - 1; i++)
      {
        nextNumber = (decimal)dataGridView1.Rows[i].Cells["priceDataGridViewTextBoxColumn"].Value;        
        sumNumbers += nextNumber;
      }

      tlblPriceTotal.Text = "Sum: " + sumNumbers.ToString();
      tlblSelectedCellsTotal.Text = "Total Selected: " + dataGridView1.SelectedCells.Count.ToString();     
    }