This classmate, first of all, the maximum value of f(x) is 4 and the minimum value is 0, so the maximum value of f(x 1)-f(x2) is 4, and then 202 1÷4=505 and 1, that is, n = 50. There is also a set of f (x1)-f (x2)+... f (xn- 1)-f (xn)+0, so n-1.