Macro to Sum ALL the rows in a column - any number of rows

I need a macro (at top of the column), to SUM all of the rows below.

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My keystrokes are:

=Sum(
{Down}
{CTRL}+{SHIFT}+{DOWN}      ' these keystrokes select all contiguous rows down (any number)
)
{RIGHT}

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Excel 2010 converts that to:

Macro1()

       Range("A1").Select
       ActiveCell.FormulaR1C1 = "=SUM(R[2]C:R[4478]C)"
       Range("B1").Select

End Sub

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How do I get VBA to sum ALL rows and not just (A2:A4478) ?