@Veronika *********
you left the country TODAY and went to cambodia?
If so that was the land border officer marking in your passport that you'd gotten one free entry by land (if indeed that was the only free entry stamp you got by land this year ๐ )
Most people are allowed TWO free 30 day entry stamps by land in a calendar year, and most borders number them when you get the stamp, guess yours decided to number the stamp when you left..