def main():
    from collections import defaultdict
    n=int(input())
    a=list(map(int,input().split()))
    d=defaultdict(int)
    for i in range(n):
        d[a[i]]+=1
    ans=0
    for i in range(1,9):
        for j in range(1,9):
            ans+=pow(i,j)*d[i]*d[j]
    print(ans)
main()