Reborn in Elementary School, I Use an Adult's Mind to Make the Whole School Laugh

1. Prologue: After pulling an all-nighter at work, the 30-year-old office worker dies from exhaustion. When he opens his eyes, he finds himself lying at a desk in an elementary school classroom. Before him are his familiar, balding homeroom teacher and his chattering childhood classmates, while in his hand is a math test marked 58.