#include <bits/stdc++.h>
#pragma optimize GCC("Ofast")
#pragma comment(linker, "/STACK:1073741824")
using namespace std;
using namespace placeholders;
const int inf = (int)1e9 + 9;
const long long linf = (long long)1e18;
const long double eps = 1e-7;
const int mod = (int)1e9 + 7;
int main() {
  ios_base::sync_with_stdio(false);
  srand(time(0));
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  vector<int> seq(n);
  for (int i = 0; i < n; i++) {
    cin >> seq[i];
  }
  vector<int> cnt1(n + 1), cnt2(n + 1);
  for (int i = 1; i <= n; i++) {
    cnt1[i] = cnt1[i - 1];
    if (seq[i - 1] == 1) {
      cnt1[i]++;
    }
  }
  for (int i = n - 1; i >= 0; i--) {
    cnt2[i] = cnt2[i + 1];
    if (seq[i] == 2) {
      cnt2[i]++;
    }
  }
  vector<vector<int> > dp(n + 2, vector<int>(n + 1, 0));
  for (int i = 1; i <= n; i++) {
    dp[i][i] = 1;
    for (int j = i + 1; j <= n; j++) {
      if (seq[j - 1] == 1) {
        dp[i][j] = max(dp[i][j - 1], cnt1[j] - cnt1[i - 1]);
      } else {
        dp[i][j] = dp[i][j - 1] + 1;
      }
    }
  }
  vector<vector<int> > dp_rev(n + 2, vector<int>(n + 1, 0));
  vector<int> seq_rev(n);
  for (int i = 0; i < n; i++) {
    seq_rev[i] = 3 - seq[i];
  }
  for (int i = 1; i <= n; i++) {
    dp_rev[i][i] = 1;
    for (int j = i + 1; j <= n; j++) {
      if (seq_rev[j - 1] == 1) {
        dp_rev[i][j] =
            max(dp_rev[i][j - 1], j - i + 1 - (cnt1[j] - cnt1[i - 1]));
      } else {
        dp_rev[i][j] = dp_rev[i][j - 1] + 1;
      }
    }
  }
  int res = 0;
  for (int i = 1; i <= n; i++) {
    int one = 0, two = 0;
    for (int j = i; j <= n; j++) {
      if (seq[j - 1] == 1) {
        one++;
      } else {
        two++;
      }
      res = max(res, dp[1][i - 1] + cnt2[j] + one);
      res = max(res, dp_rev[i][j] + cnt1[i - 1] + cnt2[j]);
      res = max(res, cnt1[i - 1] + two + dp[j + 1][n]);
    }
  }
  cout << res;
}
