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

if n == 0:
    print(0)
    exit()

# Split into runs
runs = []
current = a[0]
count = 1
for i in range(1, n):
    if a[i] == current:
        count += 1
    else:
        runs.append(count)
        current = a[i]
        count = 1
runs.append(count)

m = len(runs)
if m == 0:
    print(0)
elif m == 1:
    print(runs[0])
else:
    dp = [0] * m
    dp[0] = runs[0]
    dp[1] = max(runs[0], runs[1])
    for i in range(2, m):
        dp[i] = max(dp[i-1], dp[i-2] + runs[i])
    print(dp[m-1])