If Or statement to check cell text and delete entire row if text is found

Sub Main()
Dim lastrow As Double
lastrow = ActiveSheet.Cells(Rows.Count, "A").End(xlUp).Row

For r = lastrow to 1 step -1
    If cells(r,1).Text = "B" Or cells(r,1).Text = "M" Or cells(r,1).Text = "N" Or cells(r,1).Text = "" Then
      rows(r).Delete
    End If
Next

End Sub