#include <bits/stdc++.h>

 using namespace std;

 int dp[];

 int main()

 {

     int n, d;

     while (cin >> n)

     {

         memset(dp, , sizeof dp);

         for (int i = ; i < n; i++)

         {

             cin >> d;

             if (d == )

             {

                 dp[]++;

                 dp[] = max(dp[], dp[]) + ;

             }

             else

             {

                 dp[] = max(dp[], dp[]) + ;

                 dp[] = max(dp[], dp[]) + ;

             }

         }

         int ans = -;

         for (int i = ; i <= ; i++) ans = max(ans, dp[i]);

         cout << ans << endl;

     }

     return ;

 }