I am trying to conditional format a cell based on the total digits entered.

If I was to enter a single digit, say a '4', I would want the cell to show
'004'
If I was to enter a double digit, say a '12', I would want the cell to show
'012'
If I was to enter a triple digit, say a '351', I would want the cell to show
just '351'

I know how to do it manually, but am at a loss about autoformat/conditional
formating.