Automatically run VBA

I have the following VBA code:

Sub copycells()
ActiveWorkbook.Sheets("1-a").Select
ActiveSheet.Range("a1:c20000").Select
With Selection
.Copy
End With
ActiveWorkbook.Sheets("2-a").Select
ActiveSheet.Range("a1").Select
With Selection
.PasteSpecial (xlValues)
.PasteSpecial (xlFormats)
End With
End Sub

I want Sheet2-A to update in real time. That is, whenever I add something to 1-A, I want it to automatically execute without me having to click "Run."

Is this possible?