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

if not a:
    print(0)
    exit()

# 連続する同じ値の区間の長さを集める
current_val = a[0]
current_length = 1
segments = []
for num in a[1:]:
    if num == current_val:
        current_length += 1
    else:
        segments.append(current_length)
        current_val = num
        current_length = 1
segments.append(current_length)

# House Robberアルゴリズムで最大値を求める
prev, curr = 0, 0
for seg in segments:
    new_curr = max(curr, prev + seg)
    prev, curr = curr, new_curr

print(curr)