about "put two and two together"

[english-learner]

What does " put two and two together" mean here? Thank you!

SAM
In this particular area, yes.

MALLORY
The 18th President was Ulysses S. Grant, and the Roosevelt Room was named for Theodore.

SAM
Really?

MALLORY
There’s like a six-foot painting on the wall of Teddy Roosevelt.

SAM
I should’ve put two and two together.

MALLORY
Yes.

SAM
Look, the thing is, while there are really a great many things I can speak with
authority, I’m not good at talking about the White House.

[Marylin]

put two and two together = figure it out based on existing evidence, reason from the known facts.