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

now = 0
tmp = 0
vec = list()
for i in range(0, N):
	if now == A[i]:
		tmp = tmp + 1
	else:
		if tmp > 0:
			vec.append(tmp)
		now = A[i]
		tmp = 1
if tmp > 0:
	vec.append(tmp)

dp = [[0 for i in range(2)] for i in range(len(vec) + 1)]
for i in range(len(vec)):
	dp[i + 1][0] = max(dp[i + 1][0], dp[i][1], dp[i][0])
	dp[i + 1][1] = max(dp[i + 1][1], dp[i][0] + vec[i])
print(max(dp[-1][0], dp[-1][1]))