Datagridveiw column sum

Question

 Hi all,
I hope your all alright. I am designing a cash denomination calculator and below is the code I have used.
private void dataGridView1_CellValidated_1(object sender, DataGridViewCellEventArgs e)

  {
 
  DataGridViewRow row = dataGridView1.Rows[e.RowIndex] 
  int a = System.Convert.ToInt32(row.Cells[ColumnA.Index].Value);
  int b = System.Convert.ToInt32(row.Cells[ColumnB.Index].Value);
  int c = (a * b);
   row.Cells[ColumnC.Index].Value = c.ToString("n0");

  dataGridView1.Columns["ColumnB"].Width = 170;
  dataGridView1.Columns["ColumnC"].Width = 200;

  }

However I have failed to find a way of getting the sum of the values for all rows of column, Is there a way I can get the sum of all rows of a column of a datagridview and display it in a textbox.text or a label.text