// DP solution: try all ordering of tools used

#include <iostream>
#include <algorithm>

using namespace std;

const int MAX = 300000;
int T;
int task[MAX];

int memo[3][MAX+1];

int solve(int tool_i, int task_i, int tool[])
{
  if (task_i >= T || tool_i >= 3) {
    return 0;
  }
  
  int &ans = memo[tool_i][task_i];
  if (ans >= 0) {
    return ans;
  }

  ans = 0;
  
  // try doing this task
  if (task[task_i] == tool[tool_i]) {
    ans = max(ans, solve(tool_i, task_i+1, tool) + 1);
  }

  // try skipping
  ans = max(ans, solve(tool_i, task_i+1, tool));

  // try dropping the tool
  ans = max(ans, solve(tool_i+1, task_i, tool));

  return ans;
}

int solve(int tool[])
{
  for (int i = 0; i < 3; i++) {
    fill(memo[i], memo[i]+MAX+1, -1);
  }

  return solve(0, 0, tool);
}

int main()
{
  cin >> T;
  for (int i = 0; i < MAX; i++) {
    cin >> task[i];
  }

  int tool[3] = {0, 1, 2};
  int ans = 0;
  do {
    ans = max(ans, solve(tool));
  } while (next_permutation(tool, tool+3));

  cout << ans << endl;
  
  return 0;
}