n=int(input())
d=list(map(int, input().split()))
ans=0
for i in range(n-1):
  for j in range(i+1,n):
    ans += d[i]*d[j]
print(ans) 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 ans=0 ans 0 for i in range(n-1):
  for j in range(i+1,n):
    ans += d[i]*d[j] i range(n-1) range n-1 n 1 for j in range(i+1,n):
    ans += d[i]*d[j] j range(i+1,n) range i+1 i 1 n ans += d[i]*d[j] ans d[i]*d[j] d[i] d i d[j] d j print(ans) print ans ans=0 0 ans d=list(map(int, input().split())) list(map(int, input().split())) d n=int(input()) int(input()) n ans += d[i]*d[j] d[i]*d[j] ans
n=int(input())
d=list(map(int, input().split()))
ans=0
for i in range(n-1):
  for j in range(i+1,n):
    ans += d[i]*d[j]
print(ans)