Do you mean first or MIN ? If MIN then it is relatively easy with the MIN summary.. You'll have to trick Anaplan a little here by changing 0 to a very high value for example, 999999999, so these 0 are not picked up by MIN.
If the display of your original line item is important and you don't want to show those 99999 values, you do this on another "technical" line item and then bring the value on the original one.
technical line item (summary type MIN) = IF source value = 0 then 99999999 else source value
original line item = technical line item
If you want to display both low level values and parent MIN on the same line item you can try something like this:
As we know as per our best practice we should avoid Text line item as much as possible. I have tried to solve same problem without text line item. As we can't use any time formula like Previous etc here that's why i have used few line items to support the logic.