import java.util.*;

public class Main {
	public static void main (String[] args) {
    	Scanner sc = new Scanner(System.in);
    	int n = sc.nextInt();
    	int prev = sc.nextInt();
    	int count = 1;
    	ArrayList<Integer> list = new ArrayList<>();
    	for (int i = 1; i < n; i++) {
    	    int x = sc.nextInt();
    	    if (x == prev) {
    	        count++;
    	    } else {
    	        list.add(count);
    	        count = 1;
    	        prev = x;
    	    }
    	}
    	list.add(count);
    	int length = list.size();
    	int[][] dp = new int[2][length];
    	dp[1][0] = list.get(0);
    	for (int i = 1; i < length; i++) {
    	    dp[1][i] = Math.max(dp[0][i - 1], dp[1][i - 1] - 1) + list.get(i);
    	    dp[0][i] = Math.max(dp[0][i - 1], dp[1][i - 1]);
    	}
    	System.out.println(Math.max(dp[0][length - 1], dp[1][length - 1]));
    }
}