Hi, I could not access you picture, so I am speculating when it comes to species. There are no Kingsnakes in Korea so it may well be that you have a Ratsnake-Probably Elaphe dione.
Food for this is dependent on the size of the snake, but at the largest it would only take a small adult mouse. More likely it would feed on newly furred baby mice. Hamster would be totally wrong.
Another snake that is very similar to dione is Elaphe rufodorsata-which is a fish eater. It has a blunter snout than dione. This is also found in Korea.
What is the size of your snake? If you cannot post another picture can you give a brief discription of color, pattern and shape (is lit long and skinny or is it fat?) Are the scales rough or smooth to the touch.
As to it's gender, Does the tail widen just after the anus or does it quickly get thinner? The presence of a "hole" really means nothing. many species are dificult to sex without probing.
Hampsters are one of the worst things to offer a snake. Because of their loose skins and bad tempers, they can frequently kill or maim the attacking snake.
Frank
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"The luxury of not getting involved departed with the last lifeboat Skipper..."