#include <bits/stdc++.h>
using namespace std;
const int SI = 1e6 + 1000;
int N;
int sum2[2005], sum1[2005];
int dp[2005][2005][3];
int a[2005];
int main() {
  cin >> N;
  for (int i = 1; i <= N; i++) {
    cin >> a[i];
    if (a[i] == 1) {
      sum1[i] = sum1[i - 1] + 1;
      sum2[i] = sum2[i - 1];
    } else {
      sum1[i] = sum1[i - 1];
      sum2[i] = sum2[i - 1] + 1;
    }
  }
  if (sum1[N] == N || sum2[N] == N) {
    cout << N;
    return 0;
  }
  for (int i = 1; i <= N; i++) {
    if (sum1[i] + sum2[N] - sum2[i] == N) {
      cout << N;
      return 0;
    }
  }
  for (int i = 1; i <= N; i++)
    for (int j = i; j <= N; j++) {
      if (a[j] == 1) {
        dp[i][j][1] = ((dp[i][j - 1][2] + 1) > (dp[i][j - 1][1] + 1)
                           ? (dp[i][j - 1][2] + 1)
                           : (dp[i][j - 1][1] + 1));
        dp[i][j][2] = dp[i][j - 1][2];
      } else {
        dp[i][j][1] = dp[i][j - 1][1];
        dp[i][j][2] = dp[i][j - 1][2] + 1;
      }
    }
  int ans = 0;
  for (int i = 1; i <= N; i++)
    for (int j = i + 1; j <= N; j++) {
      if (a[i] == 2 && a[j] == 1) {
        ans = ((ans) > (sum1[i] + sum2[N] - sum2[j] + dp[i][j][1])
                   ? (ans)
                   : (sum1[i] + sum2[N] - sum2[j] + dp[i][j][1]));
      }
    }
  cout << ans;
  return 0;
}
