# Ai<8なので全組合せは少ない
# Nは大きいので同じ数が何度も出てくるのでCounter

N = int(input())
A = list(map(int, input().split()))
from collections import Counter
counted = Counter(A)
ans = 0
for num1 in counted:
    for num2 in counted:
        ans += (num1**num2)*counted[num1]*counted[num2]
print(ans)