n = int(input())
a = list(map(int, input().split()))

# Create groups of consecutive same values
groups = []
if not a:
    print(0)
    exit()
current_val = a[0]
current_len = 1
for num in a[1:]:
    if num == current_val:
        current_len += 1
    else:
        groups.append((current_val, current_len))
        current_val = num
        current_len = 1
groups.append((current_val, current_len))

m = len(groups)
dp = [0] * (m + 1)

for i in range(1, m + 1):
    val, l = groups[i-1]
    option1 = dp[i-1]  # Not choosing current group
    option2 = (dp[i-2] if i >= 2 else 0) + l  # Choosing current group, previous not chosen
    option3 = 0
    if i >= 2:
        prev_val, prev_l = groups[i-2]
        if prev_val == val:
            option3 = dp[i-1] + l  # Previous group same value and chosen
    dp[i] = max(option1, option2, option3)

print(dp[m])