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

cnt = [0 for _ in range(9)]
for i in range(n):
  cnt[a[i]] += 1

ans = 0
for x in range(1, 9):
  for y in range(1, 9):
    ans += cnt[x] * cnt[y] * (x ** y)

print(ans)