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

li0 = [x for x in range(n) if a[x] == 0]
li0 = list(reversed(li0))
ans = 0

if 0 not in a:
	print(0)
	exit()
for i in range(n-1):
	if a[i] == 0:
		ans += n - i
		if i >= li0[-1]:
			li0 = li0[:len(li0)-1]
	else:
		if len(li0) == 0:
			break
		ans += n - i - (li0[-1]-i)		
print(ans)