input()
*l,=map(int,input().split())
ans=0
for i in l:
    for j in l:
        ans+=i*j
print((ans-sum([x*y for (x, y) in zip(l,l)]))//2) input() input *l,=map(int,input().split()) *l l map(int,input().split()) map int input().split() ().split () input split ans=0 ans 0 for i in l:
    for j in l:
        ans+=i*j i l for j in l:
        ans+=i*j j l ans+=i*j ans i*j i j x*y for (x, y) in zip(l,l) for (x, y) in zip(l,l) (x, y) x y zip(l,l) zip l l for (x, y) in zip(l,l) x*y x y print((ans-sum([x*y for (x, y) in zip(l,l)]))//2) print (ans-sum([x*y for (x, y) in zip(l,l)]))//2 ans-sum([x*y for (x, y) in zip(l,l)]) ans sum([x*y for (x, y) in zip(l,l)]) sum [x*y for (x, y) in zip(l,l)] 2 ans+=i*j i*j ans ans=0 0 ans
input()
*l,=map(int,input().split())
ans=0
for i in l:
    for j in l:
        ans+=i*j
print((ans-sum([x*y for (x, y) in zip(l,l)]))//2)