from itertools import groupby
input()
_ = list(map(int, input().split()))
a = [len(tuple(v)) for _, v in groupby(_)]
N = len(a)
dp = [0]*(N+10)

for i in range(N):
    dp[i+1] = max(dp[i], dp[i+1])
    dp[i+2] = max(dp[i]+a[i], dp[i+2])

print(max(dp))