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