What about this:
=SUM(IF(MOD(ROW(A1:A14),4)=1,A1:A14,0))It checks all cells in range A1:A14, and for each of them it checks the "rest" of the row number modulo 4. In case this is 1 (this is true for the cases A1, A5, A9 and A13), the numbers are added.
Hereby an explanatory screenshot:
