#include <bits/stdc++.h>
using namespace std;
const int N = 2000 + 4;
int n, a[N];
int s[N];
int count1(int i, int j) { return s[j] - s[i - 1]; }
int count2(int i, int j) { return j - i + 1 - s[j] + s[i - 1]; }
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  s[0] = 0;
  for (int i = 1; i <= n; i++) s[i] = s[i - 1] + (a[i] == 1);
  int cnt1, cnt2;
  int ans = 0;
  for (int j = 1; j <= n; j++) {
    cnt1 = 0;
    cnt2 = 0;
    for (int i = 1; i <= j; i++) cnt1 = max(cnt1, count1(1, i) + count2(i, j));
    for (int k = j + 1; k <= n; k++)
      cnt2 = max(cnt2, count1(j + 1, k) + count2(k, n));
    ans = max(ans, cnt1 + cnt2);
  }
  cout << ans;
  return 0;
}

### Prompt

Develop a solution in cpp to the problem described below:

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 N = 2000 + 4;
int n, a[N];
int s[N];
int count1(int i, int j) { return s[j] - s[i - 1]; }
int count2(int i, int j) { return j - i + 1 - s[j] + s[i - 1]; }
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) cin >> a[i];
  s[0] = 0;
  for (int i = 1; i <= n; i++) s[i] = s[i - 1] + (a[i] == 1);
  int cnt1, cnt2;
  int ans = 0;
  for (int j = 1; j <= n; j++) {
    cnt1 = 0;
    cnt2 = 0;
    for (int i = 1; i <= j; i++) cnt1 = max(cnt1, count1(1, i) + count2(i, j));
    for (int k = j + 1; k <= n; k++)
      cnt2 = max(cnt2, count1(j + 1, k) + count2(k, n));
    ans = max(ans, cnt1 + cnt2);
  }
  cout << ans;
  return 0;
}

```