n = int(input())
c1 = c2 = 0
for a in map(int, input().split()):
    if a == 1:
        c1 += 1
    elif a == 2:
        c2 += 1
ans = n * (n - 1) // 2
ans += c1 * (n - c1) + c1 * (c1 - 1) // 2
ans += c1 * c2
print(ans)