If you divide the number by 100, you will get the student number, because you will get rid of the last two digits. If you multiply the student number by 100, you will get a number starting with the student number, and you can subtract that from the input to get the score.
Example:
S = 35578
number = 35578 // 100 = 355
score = 35578 - 35500 = 78