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.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;

/**
 * @author Don Li
 */
public class ATwistyMovement {
    void solve() {
        int n = in.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = in.nextInt();
        
        List<Integer> twos = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            if (a[i] == 2) twos.add(i);
        }
        
        int ans = Math.max(twos.size(), n - twos.size());
        
        int[] prefix_ones = new int[n + 1];
        for (int i = 0; i < n; i++) {
            prefix_ones[i + 1] = prefix_ones[i] + (a[i] == 1 ? 1 : 0);
        }
        int[] suffix_ones = new int[n + 1];
        for (int i = n - 1; i >= 0; i--) {
            suffix_ones[n - i] = suffix_ones[n - i - 1] + (a[i] == 1 ? 1 : 0);
        }
        
        for (int i : twos) {
            int lmax = prefix_ones[i], cnt = 0;
            for (int l = i - 1; l >= 0; l--) {
                if (a[l] == 2) cnt++;
                lmax = Math.max(lmax, cnt + prefix_ones[l]);
            }
            int rmax = (n - i - 1) - suffix_ones[n - i - 1];
            cnt = 0;
            for (int r = i + 1; r < n; r++) {
                if (a[r] == 1) cnt++;
                rmax = Math.max(rmax, cnt + (n - r - 1) - suffix_ones[n - r - 1]);
            }
            ans = Math.max(ans, lmax + 1 + rmax);
        }
        out.println(ans);
    }
    
    public static void main(String[] args) {
        in = new FastScanner(new BufferedReader(new InputStreamReader(System.in)));
        out = new PrintWriter(System.out);
        new ATwistyMovement().solve();
        out.close();
    }
    
    static FastScanner in;
    static PrintWriter out;
    
    static class FastScanner {
        BufferedReader in;
        StringTokenizer st;
        
        public FastScanner(BufferedReader in) {
            this.in = in;
        }
        
        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(in.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }
        
        public int nextInt() {
            return Integer.parseInt(nextToken());
        }
        
        public long nextLong() {
            return Long.parseLong(nextToken());
        }
        
        public double nextDouble() {
            return Double.parseDouble(nextToken());
        }
    }
}
