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

NOW=-1
count=0
LIST=[]

for a in A:
    if NOW==a:
        count+=1
    else:
        LIST.append((NOW,count))
        NOW=a
        count=1

DP=[0]*len(LIST)

for i in range(1,len(LIST)):
    DP[i]=max(DP[i-1],DP[i-1]-1+LIST[i][1],DP[i-2]+LIST[i][1])

print(max(DP))