Hanguk Story has got the plot.
In his dream, an American fleet invades North Korea. The protagonist and his friends try to defend by firing artillery shells made of pencils, but the protagonist doesn't know how to use protractor to aim. Overwhelmed by the evil American fleet, he wakes up from the dream. He says something along the line of "I must study hard and pay attention in class so I can be a great soldier to fight against the Americans". The rest is math lessons.Work hard, kid. Lil' Kim needs his hookers and smack.