def solve():
    N=int(input())
    A=list(map(int,input().split()))

    K=max(A)
    count=[A.count(i) for i in range(K+1)]

    ans=0
    for a in range(K+1):
        for b in range(K+1):
            ans+=count[a]*count[b]*pow(a,b)
    return ans

#==================================================
print(solve())