"This year has three hundred and sixty-six days."

Translation: Tento rok má tři sta šedesát šest dnů.

[thomasmarsh]

Shouldn't "letos" also be accepted in place of "tento rok"?

[endless_sleeper]

Nope, letos is an adverb.

[AgnusOinas]

If you said "Letos má 366 dnů", the immediate question that pops into a native speaker's head is: "Who has 366 days this year?" :)