How to sum datagridview selected cell

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C#

WinForms

Hi,
I wanna archieve something like Excel. If i select two or more cells within a column, it should display me the calculated value in a label.

Example if i highlight three cells with the values (500, 400 and 200). The label should display me 1100

My code is somehow okay but it is not displaying the summed value of the selected cells. It only display the first selected cell value.

My code:

private void datagridview1_SelectionChanged(object sender, EventArgs e)
{
  for (int i = 0; i < datagridview1.SelectedCells.Count; i++)
  {
    if (!datagridview1.SelectedCells.Contains(datagridview1.Rows[i].Cells[i]))
    {
      float nextNumber = 0;
      float sumNumbers = 0;

      if (float.TryParse(datagridview1.SelectedCells[i].FormattedValue.ToString(), out nextNumber))
        sumNumbers += nextNumber;

      label13.Text = "selected value: " + sumNumbers;
      label16.Text = "Nr.selected cell: " + datagridview1.SelectedCells.Count.ToString();
    }
    else
    {
      MessageBox.Show("Can't sum");
    }
  }