How to bulk insert only new rows in PostreSQL

I have list of products (3 million items) without IDs - only titles. But I don't know which titles already exist in DB. New products (about 2.9 million items) must be added into DB. After that I must know ID for each products (new and existing).

Is there the fastest way to do it in PostgreSQL? I can change DB as needed (add default values, add columns etc.).