Derivation is often used to find the maximum. There are two unknowns in S(x, y). Take the derivative of x first, then take the derivative of y.

and

Derive y first, then x.

The result is the same. After doing it, you will find that there is only X left. Take the value of x between 0 and 100.

Although this problem is a difficult one, it's too … I've seen countless problems to find the best value, and this problem is the most meaningless: 1. Can't be used for practical problems; You won't find it in the paper.

Unfortunately, it hasn't been solved.