This is my code of Problem D of Panasonic Programming Contest (AtCoder Beginner Contest 186).

atcoder-abc-186-d.py

# 入力
N = int(input())
A = sorted([int(x) for x in input().split()])

# 答えを格納する変数
ans = 0

# Aの累積和を格納する配列
Aruiseki = [[] for _ in range(N)]

# Aの累積和を計算しておく
Aruiseki[N-1] = A[N-1]
for i in range(N-2,-1,-1):
  Aruiseki[i] = Aruiseki[i+1] + A[i]

# Aの累積和を利用して計算する
# 配列のindexに注意
for i in range(N-1):
  ans += Aruiseki[i+1] - (N - i - 1) * A[i]

# 答えを出力
print(ans)