n = int(input())
cnt = [0] * 10
a = list(map(int,input().split()))
for i in range(n):
    cnt[a[i]] += 1
ans = 0
for i in range(1, 9):
    for j in range(1, 9):
        ans += cnt[i] * cnt[j] * pow(i,j)
print(ans)