#include <bits/stdc++.h>
using namespace std;
int dp[2005][2];
int rdp[2005][2];
int fdp[2005][2005][2];
int pref[2005][2];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  int n;
  cin >> n;
  int arr[n + 1];
  for (int i = 1; i < n + 1; i++) {
    cin >> arr[i];
    if (arr[i] == 1) {
      dp[i][0] = dp[i - 1][0] + 1;
      dp[i][1] = dp[i - 1][1];
      pref[i][1] = pref[i - 1][1];
      pref[i][0] = pref[i - 1][0] + 1;
    } else {
      dp[i][1] = max(dp[i - 1][0], dp[i - 1][1]) + 1;
      dp[i][0] = dp[i - 1][0];
      pref[i][1] = pref[i - 1][1] + 1;
      pref[i][0] = pref[i - 1][0];
    }
  }
  for (int i = n + 1 - 1; i >= 1; i--) {
    if (arr[i] == 2) {
      rdp[i][0] = rdp[i + 1][0];
      rdp[i][1] = rdp[i + 1][1] + 1;
    } else {
      rdp[i][0] = max(rdp[i + 1][0], rdp[i + 1][1]) + 1;
      rdp[i][1] = rdp[i + 1][1];
    }
  }
  int ans = max(dp[n][0], dp[n][1]);
  for (int j = 1; j < n + 1; j++) {
    for (int i = j; i < n + 1; i++) {
      if (arr[i] == 2) {
        fdp[j][i][0] = fdp[j][i - 1][0] + 1;
        fdp[j][i][1] = fdp[j][i - 1][1];
      } else {
        fdp[j][i][1] = max(fdp[j][i - 1][0], fdp[j][i - 1][1]) + 1;
        fdp[j][i][0] = fdp[j][i - 1][0];
      }
    }
  }
  for (int i = 1; i < n + 1; i++) {
    for (int j = i + 1; j < n + 1; j++) {
      int t1 = dp[i - 1][0];
      int t2 = dp[i - 1][1];
      int rt1 = rdp[j + 1][0];
      int rt2 = rdp[j + 1][1];
      int p1 = pref[j][0] - pref[i - 1][0];
      int p2 = pref[j][1] - pref[i - 1][1];
      ans = max(ans, t1 + p1 + max(rt1, rt2));
      ans = max(ans, t2 + rt2 + p2);
      ans = max(ans, t1 + rt2 + max(fdp[i][j][0], fdp[i][j][1]));
    }
  }
  cout << ans;
}
