N = int(input())
A = list(map(int, input().split()))
M = [0] * 2
m, n = 0, 0
ans = 0
i = N - 1
for a in A[::-1]:
    ans += m * a * (i != N - 1)
    m, n = n * (1 - a) + 1, m * a + 1
    # if a: m = 1
    # else: n = 1
    i -= 1
    
print(ans)