<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def sfs_scaled(dac, n=None):
 """Compute the site frequency spectrum scaled such that a constant value is expected across the spectrum for neutral variation and constant population size. Parameters dac : array_like, int, shape (n_variants,) Array of derived allele counts. n : int, optional The total number of chromosomes called. Returns ------- sfs_scaled : ndarray, int, shape (n_chromosomes,) An array where the value of the kth element is the number of variants with k derived alleles, multiplied by k. """


    # compute site frequency spectrum
    s = sfs(dac, n=n)

    # apply scaling
    s = scale_sfs(s)

    return s