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.
//package CF;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

public class A {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);
		int n = sc.nextInt();
		int [] a = new int[n];
		for (int i = 0; i < a.length; i++) {
			a[i] = sc.nextInt();
		}
		int [][] b = new int[n+1][3];
		b[n][1] = 0;
		b[n][2] = 0;
		for (int i = n-1; i >= 0; i--) {
			up2(a[i], b[i], b[i+1]);
		}
		int ans = 0;
		int [] v = new int[3];
		for (int i = 0; i < a.length; i++) {
			int [] ran = new int[3];
			for (int j = i; j < a.length; j++) {
				up2(a[j], ran, ran);
				ans = Math.max(ans, Math.max(Math.max(v[1]+ran[1]+b[j+1][1], v[1]+ran[1]+b[j+1][2]), 
						Math.max(v[1]+ran[2]+b[j+1][2], v[2]+ran[2]+b[j+1][2])));
			}
			up(a[i], v, v);
		}
		out.println(ans);
		out.flush();
		out.close();
	}
	static void up(int val, int [] a, int [] b){
		if(val == 1)
		{
			a[1] = b[1]+1;
			a[2] = b[2];
		}
		else{
			a[1] = b[1];
			a[2] = Math.max(a[1]+1, b[2]+1);
		}
	}
	static void up2(int val, int [] a, int [] b){
		if(val == 1)
		{
			a[2] = b[2];
			a[1] = Math.max(b[2]+1, b[1]+1);
			
		}
		else{
			a[2] = b[2]+1;
			a[1] = b[1];
		}
	}
	static class Scanner {
		StringTokenizer st;
		BufferedReader br;

		public Scanner(InputStream s) {
			br = new BufferedReader(new InputStreamReader(s));
		}

		public Scanner(FileReader fileReader) {
			br = new BufferedReader(fileReader);
		}

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens())
				st = new StringTokenizer(br.readLine());
			return st.nextToken();
		}

		public int nextInt() throws IOException {
			return Integer.parseInt(next());
		}

		public long nextLong() throws IOException {
			return Long.parseLong(next());
		}

		public String nextLine() throws IOException {
			return br.readLine();
		}

		public boolean ready() throws IOException {
			return br.ready();
		}
	}
}