def Run_Length(lst):
    run_length=[]
    if lst:
        prev=lst[0]
        cnt=1
        for x in lst[1:]:
            if x==prev:
                cnt+=1
            else:
                run_length.append((prev,cnt))
                prev=x
                cnt=1
        run_length.append((prev,cnt))
    return run_length

N=int(input())
A=Run_Length(list(map(int,input().split())))
le=len(A)
inf=1<<30
dp0,dp1=0,-inf
for a,c in A:
    dp0,dp1=max(dp0,dp1),dp0+c
ans=max(dp0,dp1)
print(ans)