Coordinate vertice alto sinistro di una cella di Datagrid

Point GetCellPointUpLeft(Point p)
{
 int finalx = tuoDataGridView.ColumnHeadersHeight;
 int finaly = tuoDataGridView.RowHeadersWidth;
 foreach (DataGridViewColumn column in tuoDataGridView.Columns)
 {
  if (p.X > finalx + column.Width)
  {
   finalx += column.Width;
  }
  else
  {
   break;
  }
 }
 foreach (DataGridViewRow row in tuoDataGridView.Rows)
 {
  if (p.Y > finaly + row.Height)
  {
   finaly += row.Height;
  }
  else
  {
   break;
  }
 }
return new Point(finalx, finaly);
}