I, personally, find feedback nodes more complicated than a "Do Once" While Loop with a Shift Register that "remembers" the previous call. You make it "do once" by wiring a True constant to its Stop terminal. Here's a picture (I know, I say "Don't post pictures ...", but I wanted to put in a label ...
I hope this isn't the first time you've seen something like this. If it is, just try to code it up and run it a few times, putting an indicator on the Shift Register terminal shown as "Last Input". If you run with Highlight Execution (the little light-bulb) turned on, it should be crystal clear how this works.
Bob Schor