N = int(input())
A = tuple(map(int, input().split()))

ans = 0
for start in (0, 1):
    tmp = 0
    for i in range(start, N, 2):
        if A[i] == 1:
            tmp += 1
            ans += tmp
        else:
            tmp = 0
        if i + 1 < N:
            if A[i + 1] == 0:
                ans += tmp
            else:
                tmp = 0
    ans -= tmp
print(ans)