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 codeforces.R462;

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


public class C
{
	public static void main(String[] args) throws IOException
	{
		Scanner sc = new Scanner(System.in);
		PrintWriter pw = new PrintWriter(System.out);
		
		int n = sc.nextInt();
		int[] arr = new int[n];
		for (int i = 0; i < n; i++)
			arr[i] = sc.nextInt();
		
		int cum1[] = new int[n];
		int cum2[] = new int[n];
		int Dec[][] = new int[n][n];
		int Inc[][] = new int[n][n];
		
		for (int i = 0; i < n; i++)
		{
			if(arr[i] == 1)
				cum1[i]++;
			else
				cum2[i]++;
			
			if(i > 0)
			{
				cum1[i] += cum1[i-1];
				cum2[i] += cum2[i-1];
			}
		}
		
		// 2 -> 1
		for (int i = 0; i < n; i++)
			for (int j = i; j < n; j++)
			{
				if(i == j)
					Dec[i][j] = 1;
				else
				{
					if(arr[j] == 1)
						Dec[i][j] = Dec[i][j-1]+1;
					else
					{
						int cnt2 = cum2[j];
						if(i > 0)
							cnt2 -= cum2[i-1];
						Dec[i][j] = Math.max(Dec[i][j-1], cnt2);
					}
				}
			}
		
		// 1 -> 2
		for (int i = 0; i < n; i++)
			for (int j = i; j < n; j++)
			{
				if(i == j)
					Inc[i][j] = 1;
				else
				{
					if(arr[j] == 2)
						Inc[i][j] = Inc[i][j-1]+1;
					else
					{
						int cnt1 = cum1[j];
						if(i > 0)
							cnt1 -= cum1[i-1];
						Inc[i][j] = Math.max(Inc[i][j-1], cnt1);
					}
				}
			}
		
		int mx = 0;
		for (int i = 0; i < n; i++)
			for (int j = i; j < n; j++)
			{
				int onesBefore = 0;
				if(i > 0)
					onesBefore = cum1[i-1];
				int twosAfter = cum2[n-1] - cum2[j];
				int incBefore = 0;
				int onesHere = cum1[j];
				if(i > 0) onesHere -= cum1[i-1];
				if(i > 0)
					incBefore = Inc[0][i-1];
				int twosHere = cum2[j];
				if(i > 0) twosHere -= cum2[i-1];
				int decHere = Dec[i][j];
				
				int incAfter = 0;
				if(j < n-1)
					incAfter = Inc[j+1][n-1];
				mx = Math.max(mx, onesBefore+onesHere+incAfter);
				mx = Math.max(mx, onesBefore+decHere+twosAfter);
				mx = Math.max(mx, incBefore+twosHere+twosAfter);
				
				
			}
		
		System.out.println(mx);
		
		pw.flush();
		pw.close();
	}
	
	
	static int[][] packD(int n, int[] from, int[] to) {
		int[][] g = new int[n][];
		int[] p = new int[n];
		for (int f : from) p[f]++;
		for (int i = 0; i < n; i++) g[i] = new int[p[i]];
		for (int i = 0; i < from.length; i++) {g[from[i]][--p[from[i]]] = to[i];}
		return g;
	}
	static class Scanner 
	{
		StringTokenizer st; BufferedReader br;
		public Scanner(InputStream s){	br = new BufferedReader(new InputStreamReader(s));}
		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();}
	}
}
