Calculate the exp to award players for the encounter

[Engeven]

For parties with size other than 4, awarded exp is different than calculated exp. Could you display exp to award for an encounter in calculations? For example: 5man party of level 1, against 5 giant rats have 100xp (since each rat is 20xp) however when rewarding exp, you give 80xp instead of 100xp.

I have no idea how to formulate this programmatically (I'm fairly new to pf2e with no experience) but I'm copy pasting the relevant rules from Core Rule book.

Different Party Sizes (CRB 489)
For each additional character in the party beyond the
fourth, increase your XP budget by the amount shown
in the Character Adjustment value for your encounter in
Table 10–1: Encounter Budget. If you have fewer than
four characters, use the same process in reverse: for each
missing character, remove that amount of XP from your
XP budget. Note that if you adjust your XP budget to
account for party size, the XP awards for the encounter
don’t change—you’ll always award the amount of XP
listed for a group of four characters.

PARTY SIZE (CRB 508)
The rules for advancement assume a group of four PCs.
The rules for encounters (page 489) describe how to
accommodate groups of a different size, but the XP awards
don’t change—always award the amount of XP listed for a
group of four characters.