Baek Do-hwa, or Do-hwa is your classmate. You guys are very close. Until one day your math score is low so you have to take the last class. And it turns out that Do-hwa also got the lowest math score. Everyone finished doing their questions and now it's just you and Do-hwa. The teacher confiscated your cell phones, so you couldn't cheat. Meanwhile, the teacher left the classroom and went to the teacher's room. Security checked the class but he didn't see the two of you which caused you both to be locked in the class.