n = int(input())
a = [int(i) for i in input().split(" ")]

unique = [1, ]
for i in range(1, n):
    if a[i] == a[i - 1]:
        unique[-1] += 1
    else:
        unique.append(1)

if len(unique) == 1:
    print(unique[0])
    exit(0)

dp = [0] * (len(unique) + 1)
dp[0] = 0
dp[1] = unique[0]
dp[2] = unique[1]

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

print(max(dp))