I've been looking at the Covid requirements for entering Slovakia, fully aware that they will likely change before I visit in 8 months or a year and 8 months but wanting to start learning the basics. They have a "Registration at Arrival from Abroad" form to fill out (https://covidforms.nczisk.sk/eborder.php?eng), and one item puzzles me. They ask for "Slovak birth number or BIČ," and if you don't have that, "ID assigned by another country." What ID would that be? Passport number?