n = int(input())
d = list(map(int, input().split()))

s = 0

for i in range(n):
    for j in range(n):
        if i < j:
            s += (d[i] * d[j])

print(s) n = int(input()) n int(input()) int input() input d = list(map(int, input().split())) d list(map(int, input().split())) list map(int, input().split()) map int input().split() ().split () input split s = 0 s 0 for i in range(n):
    for j in range(n):
        if i < j:
            s += (d[i] * d[j]) i range(n) range n for j in range(n):
        if i < j:
            s += (d[i] * d[j]) j range(n) range n if i < j:
            s += (d[i] * d[j]) i < j i j s += (d[i] * d[j]) s d[i] * d[j] d[i] d i d[j] d j print(s) print s s += (d[i] * d[j]) d[i] * d[j] s d = list(map(int, input().split())) list(map(int, input().split())) d n = int(input()) int(input()) n s = 0 0 s
n = int(input())
d = list(map(int, input().split()))

s = 0

for i in range(n):
    for j in range(n):
        if i < j:
            s += (d[i] * d[j])

print(s)