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

ans = 0

for i in range(0,n):
    for j in range(0,n):
        if i >= j:
            continue
        else:
            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(0,n):
    for j in range(0,n):
        if i >= j:
            continue
        else:
            ans += d[i]*d[j] i range(0,n) range 0 n for j in range(0,n):
        if i >= j:
            continue
        else:
            ans += d[i]*d[j] j range(0,n) range 0 n if i >= j:
            continue
        else:
            ans += d[i]*d[j] i >= j i j continue 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(0,n):
    for j in range(0,n):
        if i >= j:
            continue
        else:
            ans += d[i]*d[j]
print(ans)