#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n;
  cin >> n;
  vector<long long> arr(n);
  for (auto &i : arr) cin >> i;
  vector<long long> pref(n), suff(n);
  long long curr1 = 0;
  for (int i = 0; i < n; ++i) {
    pref[i] = curr1;
    curr1 += (arr[i] == 1);
  }
  long long curr2 = 0;
  for (int i = n - 1; i >= 0; --i) {
    suff[i] = curr2;
    curr2 += (arr[i] == 2);
  }
  long long ans = 0;
  for (long long r = 0; r < n; ++r) {
    ans = max(ans, pref[r] + suff[r] + 1);
    curr1 = 0, curr2 = 0;
    for (long long l = r; l >= 0; --l) {
      if (arr[l] == 2)
        curr2 = max(curr2, curr1) + 1;
      else
        ++curr1;
      ans = max(ans, curr2 + pref[l] + suff[r]);
    }
  }
  cout << ans;
  return 0;
}

### Prompt

Please create a solution in cpp 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;
int main() {
  long long n;
  cin >> n;
  vector<long long> arr(n);
  for (auto &i : arr) cin >> i;
  vector<long long> pref(n), suff(n);
  long long curr1 = 0;
  for (int i = 0; i < n; ++i) {
    pref[i] = curr1;
    curr1 += (arr[i] == 1);
  }
  long long curr2 = 0;
  for (int i = n - 1; i >= 0; --i) {
    suff[i] = curr2;
    curr2 += (arr[i] == 2);
  }
  long long ans = 0;
  for (long long r = 0; r < n; ++r) {
    ans = max(ans, pref[r] + suff[r] + 1);
    curr1 = 0, curr2 = 0;
    for (long long l = r; l >= 0; --l) {
      if (arr[l] == 2)
        curr2 = max(curr2, curr1) + 1;
      else
        ++curr1;
      ans = max(ans, curr2 + pref[l] + suff[r]);
    }
  }
  cout << ans;
  return 0;
}

```