No, that F doesn’t stand for first floor. You see, in Korea, the number 13 is nothing special because all the superstition is reserved for the number 4.
This is because the word for the number 4 also sounds like the word for death. Thankfully, the superstition isn’t so hysterical where the number 4 is taken off keyboards or cellphone keypads or calculators.
It must be only bad luck for a floor in a building to be called 4. Now I wonder if they have their own Friday the Fourth spookiness.