Converting monthly data into quarterly

Dear Excel experts,

I need to convert several series of monthly data (in rows, one range from Oct 1994-June 2009, i.e., in my sheet columns HD:NZ) into Quarterly data.

The Quarterly result should simply be the last month of that Quarter, so for Jan-Mar it should return March for Q1, Apr-Jun should return June for Q2, etcetera. There is, however, one caveat: if a quarter's last month does not contain any data or a value of '0' it should return the data for either the first or second preceding month. In the above examples: for Q1 either February or January, for Q2 either May or April.

Any tips? (No pivot tables or VBA please).

Many thanks in advance for your kind support!

Best regards,

Paul