Kendrick Lamar: Prez Obama Gets Message in My Song ... Live Forever with Just $1

Kendrick Lamar's found the fountain of youth, and it's been hiding in the K Dot track President Obama declared the year's best ... "How Much a Dollar Cost."

Kendrick told us what he thought of Obama's high praise, and then got philosophical with us about his song. There's a lot here -- should you hand out cash to the homeless? Who are you really helping if you do that?

Our photog, Jake, chopped it up with Kendrick and the answer is ... immortality, possibly. Real talk.

Open your mind and watch ... it's deep.