N = int(input())
A = list(map(int,input().split()))

katamari = []
kosu = 1#ある数字のかたまりに含まれる，その数字の個数
prev = None#直前の値
for a in A:
    if a == prev:
        kosu += 1
    else:
        katamari.append(kosu)
        prev = a
        kosu = 1
katamari.append(kosu)

katamari = katamari[1:]
#print(katamari)

if len(katamari) > 1:
    dp = [katamari[0],katamari[1]] + [0]*(len(katamari)-2)#その位置を採用したときの最大値
    for i in range(2,len(katamari)):
        dp[i] = dp[i-2] + katamari[i]
        try:
            dp[i] = max(dp[i], dp[i-3] + katamari[i])
        except IndexError:
            pass
    #print(dp)
    print(dp[-1])
else:
    print(katamari[0])