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

# Generate runs
runs = []
if not a:
    print(0)
    exit()
current_val = a[0]
current_length = 1
for num in a[1:]:
    if num == current_val:
        current_length += 1
    else:
        runs.append(current_length)
        current_val = num
        current_length = 1
runs.append(current_length)

if len(runs) == 0:
    print(0)
    exit()

# Dynamic programming
prev_take = runs[0]
prev_notake = 0

for i in range(1, len(runs)):
    current_take = prev_notake + runs[i]
    current_notake = max(prev_take, prev_notake)
    prev_take, prev_notake = current_take, current_notake

print(max(prev_take, prev_notake))