How can I set an InputBox default value to the active worksheet's LeftHeader?

More infor - if needed:
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I have a workbook with several worksheets.
Each sheet has the same page setup except for the LeftHeader.

Instead of using FilePageSetup on every sheet I select each sheet then run
a macro that uses an InputBox to prompt for the LeftHeader and reset it.

This works OK except the InputBox value is initially <blank

What I would really like to do is to set the InputBox default value to the
existing LeftHeader value. This way I don't have to re-type the header in
full when, for example, I only want to correct a spelling mistake.