import sys
input = sys.stdin.readline
from collections import *

N = int(input())
A = list(map(int, input().split()))
cnt = [0]*9

for Ai in A:
    cnt[Ai] += 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)