After his mother's death, 16-year-old Hyung-ju suspects that his father is not his biological father. A secret paternity test reveals that he is not. Confused, he uses his math skills to figure out his biological father and embarks on a journey with his best friend, Ji-su, to find him.
| Actor | Role |
|---|---|
| JJeong Da-minHyung-ju | Hyung-ju |
 Kim Se-wonJi-su | Ji-su |
 Kwak Min-kyuMin-hyu | Min-hyu |
| LLee Gi-munNot listed | Not listed |
 Seo Suk-kyuNot listed | Not listed |
| KKim Il-duNot listed | Not listed |
 Woo Yeon-seoMin-joo | Min-joo |
 Kim Min-seoNot listed | Not listed |
 Shin Ki-hwanNot listed | Not listed |
 Kim Jae-uNot listed | Not listed |