Which Shard Made This

Instagram generates 64 bit ids inside Postgres rather than from a separate id service. The layout is 41 bits of milliseconds since a custom epoch, then 13 bits of logical shard id, then 10 bits of per-table sequence taken modulo 1024. Every logical shard is a schema carrying its own copy of this function:

CREATE OR REPLACE FUNCTION insta5.next_id(OUT result bigint) AS $$
DECLARE
    our_epoch  bigint := 1314220021721;
    seq_id     bigint;
    now_millis bigint;
    shard_id   int := 5;
BEGIN
    SELECT nextval('insta5.table_id_seq') % 1024 INTO seq_id;
    SELECT FLOOR(EXTRACT(EPOCH FROM clock_timestamp()) * 1000) INTO now_millis;
    result := (now_millis - our_epoch) << 23;
    result := result | (shard_id << 10);
    result := result | (seq_id);
END;
$$ LANGUAGE PLPGSQL;

A photo row carries id 8388608001263623. Which logical shard produced it?