The total surplus is from high school. According to relevant data, the department of complete surplus belongs to high school because it is in the content of elective course 4-6 of high school mathematics in People's Education Edition B. Take a number from each residue class of module n and get a set of n numbers, which is called the complete residue system of module n. The complete residue system is often used to prove its existence in number theory. If an element is defined in the residue class of module n, then the number of n constitutes the complete residue system of module n.