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