from collections import defaultdict
n = int(input())
l = list(map(int,input().split()))

a = defaultdict(int)
for element in l: 
    a[element] = a.get(element, 0) + 1 

z = 0 
for i in range(1, 9): 
    for j in range(1, 9): 
        z += a[i] * a[j] * (i ** j) 
print(z)