Copying a formula problem

Hi All,
I have a small question.

Knipsel.PNG

If I select A1 to A3 (example 1) and copy it to A4, the formula in A4 becomes =+C4 (example 2)

How can I chance this so when I copy this the formula becomes =+C2 and not =+C4

Maybe try this in cell A1 and copy to A4, A7, etc.
=OFFSET($C$1,(ROW()/3),0)

This works great, thank you !!