#include <bits/stdc++.h>   using namespace std;   const int MAX = 2e3 + 1;   int dp[MAX][4], in[MAX];   int main() {     ios::sync_with_stdio(0);     int n, ans = 1;     cin >> n;     for (int i = 0; i < n; ++i) {       cin >> in[i];       if (in[i] == 1)         dp[i][0] = 1;       else         dp[i][1] = 1;       for (int j = 0; j < i; ++j) {         if (in[i] == 1 && in[j] == 1) {           dp[i][0] = max(dp[i][0], dp[j][0] + 1);           dp[i][2] = max(dp[i][2], dp[j][2] + 1);         }         if (in[i] == 2 && in[j] == 2) {           dp[i][1] = max(dp[i][1], dp[j][1] + 1);           dp[i][3] = max(dp[i][3], dp[j][3] + 1);         }         if (in[i] == 1 && in[j] == 2) {           dp[i][2] = max(dp[i][2], dp[j][1] + 1);         }         if (in[i] == 2 && in[j] == 1) {           dp[i][1] = max(dp[i][1], dp[j][0] + 1);           dp[i][3] = max(dp[i][3], dp[j][2] + 1);         }       }       for (int j = 0; j < 4; ++j) ans = max(ans, dp[i][j]);     }     cout << ans << endl;     return 0;   }   