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

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

# Segment the array into blocks of consecutive same values
blocks = []
current_val = a[0]
count = 1
for val in a[1:]:
    if val == current_val:
        count += 1
    else:
        blocks.append(count)
        current_val = val
        count = 1
blocks.append(count)

# Dynamic programming to find the maximum sum of non-adjacent blocks
prev_not_take = 0
prev_take = 0

for length in blocks:
    current_not_take = max(prev_not_take, prev_take)
    current_take = prev_not_take + length
    prev_not_take, prev_take = current_not_take, current_take

print(max(prev_not_take, prev_take))