#include <bits/stdc++.h>
using namespace std;
const int MAX = 2e3 + 5;
int arr[MAX];
int twos[MAX][MAX], ones[MAX][MAX];
int n;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = int(1); i < int(n + 1); i++) {
    cin >> arr[i];
  }
  for (int i = int(1); i < int(n + 1); i++) {
    for (int j = int(i); j < int(n + 1); j++) {
      ones[i][j] = ones[i][j - 1] + (arr[j] == 1);
      twos[i][j] = twos[i][j - 1] + (arr[j] == 2);
    }
  }
  int ans = 0;
  for (int i = int(1); i < int(n + 1); i++) {
    ans = max(ans, ones[1][i - 1] + twos[i][n]);
    ans = max(ans, ones[1][i] + twos[i + 1][n]);
  }
  for (int i = int(1); i < int(n + 1); i++) {
    int dp_ones = 0, dp_twos = 0;
    for (int j = int(i); j < int(n + 1); j++) {
      if (arr[j] == 1) {
        dp_ones = max(dp_ones, dp_twos) + 1;
      } else {
        dp_twos++;
      }
      int cur = ones[1][i - 1] + twos[j + 1][n] + max(dp_ones, dp_twos);
      ans = max(ans, cur);
    }
  }
  cout << ans << endl;
  return 0;
}

### Prompt

Your challenge is to write a CPP solution to the following problem:

A dragon symbolizes wisdom, power and wealth. On Lunar New Year's Day, people model a dragon with bamboo strips and clothes, raise them with rods, and hold the rods high and low to resemble a flying dragon.

A performer holding the rod low is represented by a 1, while one holding it high is represented by a 2. Thus, the line of performers can be represented by a sequence a1, a2, ..., an.

Little Tommy is among them. He would like to choose an interval [l, r] (1 ≤ l ≤ r ≤ n), then reverse al, al + 1, ..., ar so that the length of the longest non-decreasing subsequence of the new sequence is maximum.

A non-decreasing subsequence is a sequence of indices p1, p2, ..., pk, such that p1 < p2 < ... < pk and ap1 ≤ ap2 ≤ ... ≤ apk. The length of the subsequence is k.

Input

The first line contains an integer n (1 ≤ n ≤ 2000), denoting the length of the original sequence.

The second line contains n space-separated integers, describing the original sequence a1, a2, ..., an (1 ≤ ai ≤ 2, i = 1, 2, ..., n).

Output

Print a single integer, which means the maximum possible length of the longest non-decreasing subsequence of the new sequence.

Examples

Input

4
1 2 1 2


Output

4


Input

10
1 1 2 2 2 1 1 2 2 1


Output

9

Note

In the first example, after reversing [2, 3], the array will become [1, 1, 2, 2], where the length of the longest non-decreasing subsequence is 4.

In the second example, after reversing [3, 7], the array will become [1, 1, 1, 1, 2, 2, 2, 2, 2, 1], where the length of the longest non-decreasing subsequence is 9.

### Response

```cpp
#include <bits/stdc++.h>
using namespace std;
const int MAX = 2e3 + 5;
int arr[MAX];
int twos[MAX][MAX], ones[MAX][MAX];
int n;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  for (int i = int(1); i < int(n + 1); i++) {
    cin >> arr[i];
  }
  for (int i = int(1); i < int(n + 1); i++) {
    for (int j = int(i); j < int(n + 1); j++) {
      ones[i][j] = ones[i][j - 1] + (arr[j] == 1);
      twos[i][j] = twos[i][j - 1] + (arr[j] == 2);
    }
  }
  int ans = 0;
  for (int i = int(1); i < int(n + 1); i++) {
    ans = max(ans, ones[1][i - 1] + twos[i][n]);
    ans = max(ans, ones[1][i] + twos[i + 1][n]);
  }
  for (int i = int(1); i < int(n + 1); i++) {
    int dp_ones = 0, dp_twos = 0;
    for (int j = int(i); j < int(n + 1); j++) {
      if (arr[j] == 1) {
        dp_ones = max(dp_ones, dp_twos) + 1;
      } else {
        dp_twos++;
      }
      int cur = ones[1][i - 1] + twos[j + 1][n] + max(dp_ones, dp_twos);
      ans = max(ans, cur);
    }
  }
  cout << ans << endl;
  return 0;
}

```