You could try something like the following. The first step I did to generate the test data. The second I based on something "stolen" from one of Frank's solutions in the beginner's forum a couple of days ago.
This can get you started. Expect a better solution later from San Jose.
I've included both positive and negative signs (and tested their production). I've not bothered chopping the leading zeros, because I suspect there is no need, and it gives you something to do if you are keen and feel it necessary.
If all you want is a grand total of all the FI values, then Bill's TRAILER1 solution should do it. If you want something else, you need to explain more clearly what you want.
If you're not familiar with DFSORT and DFSORT's ICETOOL, I'd suggest reading through "z/OS DFSORT: Getting Started". It's an excellent tutorial, with lots of examples, that will show you how to use DFSORT, DFSORT's ICETOOL and DFSORT Symbols. You can access it online, along with all of the other DFSORT books, from: