n = int(input())
a = list(map(int, input().split()))
cnt = 0
cur = 0
for i in range(n):
	if i > 0 and a[i] != a[i - 1]:
		cnt += cur
	elif i > 0:
		cnt += cur
		cur = 0
	if a[i] == 1: cur += 1
print(cnt)