from itertools import groupby

N, *A = map(int, open(0).read().split())

G = [len(tuple(v)) for _, v in groupby(A)]

a, b, c = 0, 0, 0
for i, g in enumerate(G):
    c = max(a + g, b + g - 1)
    a, b, c = b, c, 0

print(b)