Cells in a range are all not blank, return maximum value (date), If 1 blank return 0

Hello

I've written the below formula so far but seem to be coming back a bit stuck, I've tried & and : for the range and I think I'm going around in circles. So I'm asking for a bit of help please.

=IF(S255&S256&S257&S258=" ", " ", MAX(S255&S256&S257&S258))

I'm trying to bring back the maximum value once all the cells in this 4 cell range are filled in.
If one of these cells is blank I would like it to report back nothing, and ignore the maximum total.

ie. - I only would like it to return a maximum value once all the 4 fields have a date in them

Help is always appreciated.

Thanks
Matt

Brilliant, Thank you