n = int(input())
a = list(map(int, input().split()))

s = [0 for _ in range(n + 1)]
for i in range(n):
  s[i + 1] = s[i] + a[i]

ans = - sum((n - l) * s[l] for l in range(n)) + sum(r * s[r] for r in range(1, n + 1))
print(ans)