Как суммировать данные datagridview

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Я объединил данные столбца 1 и столбца 2 Datagridview, но теперь я хочу суммировать столбец 3, столбец 4 и столбец 5 в соответствии с объединенным столбцом.

Что я уже пробовал:

Private Sub DataGridView2_CellPainting(sender As Object, e As DataGridViewCellPaintingEventArgs) Handles DataGridView2.CellPainting
        If e.ColumnIndex = 0 AndAlso e.RowIndex <> -1 Then

            Using gridBrush As Brush = New SolidBrush(Me.DataGridView2.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)

                Using gridLinePen As Pen = New Pen(gridBrush)
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds)

                    If e.RowIndex < DataGridView2.Rows.Count - 2 AndAlso DataGridView1.Rows(e.RowIndex + 1).Cells(e.ColumnIndex).Value.ToString() <> e.Value.ToString() Then
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                    End If

                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom)

                    If Not e.Value Is Nothing Then
                        If e.RowIndex > 0 AndAlso DataGridView2.Rows(e.RowIndex - 1).Cells(e.ColumnIndex).Value.ToString() = e.Value.ToString() Then
                        Else
                            e.Graphics.DrawString(CType(e.Value, String), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + 2, e.CellBounds.Y + 5, StringFormat.GenericDefault)
                        End If
                    End If

                    e.Handled = True
                End Using
            End Using
        End If
        If e.ColumnIndex = 1 AndAlso e.RowIndex <> -1 Then

            Using gridBrush As Brush = New SolidBrush(Me.DataGridView2.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)

                Using gridLinePen As Pen = New Pen(gridBrush)
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds)

                    If e.RowIndex < DataGridView2.Rows.Count - 2 AndAlso DataGridView1.Rows(e.RowIndex + 1).Cells(e.ColumnIndex).Value.ToString() <> e.Value.ToString() Then
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                    End If

                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom)

                    If Not e.Value Is Nothing Then
                        If e.RowIndex > 0 AndAlso DataGridView2.Rows(e.RowIndex - 1).Cells(e.ColumnIndex).Value.ToString() = e.Value.ToString() Then
                        Else
                            e.Graphics.DrawString(CType(e.Value, String), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + 2, e.CellBounds.Y + 5, StringFormat.GenericDefault)
                        End If
                    End If

                    e.Handled = True
                End Using
            End Using
        End If
        If e.ColumnIndex = 4 AndAlso e.RowIndex <> -1 Then

            Using gridBrush As Brush = New SolidBrush(Me.DataGridView2.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)

                Using gridLinePen As Pen = New Pen(gridBrush)
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds)

                    If e.RowIndex < DataGridView2.Rows.Count - 2 AndAlso DataGridView1.Rows(e.RowIndex + 1).Cells(e.ColumnIndex).Value.ToString() <> e.Value.ToString() Then
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                    End If
                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom)

                    If Not e.Value Is Nothing Then
                        If e.RowIndex > 0 AndAlso DataGridView2.Rows(e.RowIndex - 1).Cells(e.ColumnIndex).Value.ToString() = e.Value.ToString() Then
                        Else
                            e.Graphics.DrawString(CType(e.Value, String), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + 2, e.CellBounds.Y + 5, StringFormat.GenericDefault)
                        End If
                    End If

                    e.Handled = True
                End Using
            End Using
        End If
        If e.ColumnIndex = 2 AndAlso e.RowIndex <> -1 Then

            Using gridBrush As Brush = New SolidBrush(Me.DataGridView2.GridColor), backColorBrush As Brush = New SolidBrush(e.CellStyle.BackColor)

                Using gridLinePen As Pen = New Pen(gridBrush)
                    e.Graphics.FillRectangle(backColorBrush, e.CellBounds)
                    If e.RowIndex < DataGridView2.Rows.Count - 2 AndAlso DataGridView1.Rows(e.RowIndex + 1).Cells(e.ColumnIndex).Value.ToString() <> e.Value.ToString() Then
                        e.Graphics.DrawLine(gridLinePen, e.CellBounds.Left, e.CellBounds.Bottom - 1, e.CellBounds.Right - 1, e.CellBounds.Bottom - 1)
                    End If
                    e.Graphics.DrawLine(gridLinePen, e.CellBounds.Right - 1, e.CellBounds.Top, e.CellBounds.Right - 1, e.CellBounds.Bottom)
                    If Not e.Value Is Nothing Then
                        If e.RowIndex > 0 AndAlso DataGridView2.Rows(e.RowIndex - 1).Cells(e.ColumnIndex).Value.ToString() = e.Value.ToString() Then
                        Else
                            e.Graphics.DrawString(CType(e.Value, String), e.CellStyle.Font, Brushes.Black, e.CellBounds.X + 2, e.CellBounds.Y + 5, StringFormat.GenericDefault)
                        End If
                    End If

                    e.Handled = True
                End Using
            End Using
        End If
    End Sub

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