The inflation pool is (number of lumens in existence)*(weekly inflation rate) + fee pool. And I know that I need to have more than 0.05% of existing Lumens to receive inflation without joining inflation pool. So what's existing lumen? If anyone can clarify, would be appreciated.
I don't know how this value is exactly determined*, but the value is stored in each ledger and you can query it from horizon _embeded.records.total_coins in https://horizon.stellar.org/ledgers/?order=desc&limit=1
(* There seems to be a difference to sum(accounts.balance) from my stellar-core database. Can anyone explain that?)