N = int(input())
lsA = list(map(int,input().split()))
ll = []
cnt = 1

for i in range(1,N):
    if lsA[i-1] == lsA[i]:
        cnt += 1
    else:
        ll.append(cnt)
        cnt = 1
ll.append(cnt)
NN = len(ll)
dp = [[0,0] for i in range(NN+1)]

for i in range(1,NN+1):
    v = ll[i-1]
    dp[i][0] = max(dp[i-1][1],dp[i-1][0])
    dp[i][1] = dp[i-1][0]+v

ans = 0
for i in range(NN+1):
    ans = max(ans,max(dp[i]))
print(ans)