func_code_string: #include <bits/stdc++.h>   const int N = 2e3 + 9;   using namespace std;   int n, dp[5][N], a[N], b[5] = {0, 1, 2, 1, 2};   int main() {     scanf( %d , &n);     for (int i = 1; i <= n; i++) {       scanf( %d , &a[i]);     }     for (int i = 1; i <= 4; i++) {       for (int j = 1; j <= n; j++) {         dp[i][j] = max(dp[i - 1][j], dp[i][j - 1] + (a[j] == b[i]));       }     }     printf( %d n , dp[4][n]);     return 0;   }   