Sum over hypercube

Let $n$ be a positive integer, and suppose $a = a_1, \dots, a_{2019}$ is a sequence of integers each ranging from $1,\dots,n$. Determine the sum of $$\sum_a \frac{a_1 - a_2 + a_3 + \dots -a_{2018} + a_{2019}}{a_1 + \dots + a_{2019}}$$ Where the sum is taken over all possible sequences in that range.