from itertools import groupby

n, *a = map(int, open(0).read().split())
g = [len(list(g)) for k, g in groupby(a)]
ans1 = ans2 = 0
for i, v in enumerate(g):
	if i % 2:
		ans1 += v
		ans2 += max(v - 2, 0)
	else:
		ans1 += max(v - 2, 0)
		ans2 += v
if g[0] > 1:
	ans1 += 1
if g[-1] > 1:
	if len(g) % 2:
		ans2 += 1
	else:
		ans1 += 1
print(max(ans1, ans2))