Dynamic pointing to a cell

[pablito]

Hi !
This is my problem.
I have my data in a column in this way

A1 initially empty
A2 first value, say 100
A3 a value that should be added to A2
A4 A2+A3

I've then written a macro that puts in
A5 a blank cell
A6 the formula =A4+A5

Then I write in A5 a value and I get in A6 A4+A5 i.e. A2+A3+A5



I'd like to know if there is a formula or a macro that automatically
will copy the last value of this column in A1.

TNX and I apologize for my poor English !