How to Check if exists value and return cell

I have this problem... I have a worksheet that needs to be analised and then return the last date that has some kind of value

.......A.................B.................C.................D.................E.....................F
1/12/2011 | 2/12/2011 | 3/12/2011 | 4/12/2011 | 5/12/2011 | 6/12/2011 | ... ...
.........................75%.............32%

Has you can see cell A it's empty bellow the date, cell B has value and C has value, the other don't, but they will have when there is value for that day
In this case the last cell with value it's C

Let's say that in X cell I need to have a formula (that cannot be VBA) that I would have to return the date: 3/12/2011 because it's the last one that has value bellow.
How can I do that? I was using ISBLANK... but got nowere.

Can you help please?