99
1
3
2
2
3
1
1
3
3
3
3
3
3
1
1
3
3
3
3
1
1
3
2
1
1
1
1
1
1
1
3
2
2
2
1
3
3
1
1
3
2
1
3
3
1
2
3
3
3
1
2
2
2
3
3
3
3
3
3
2
2
2
2
3
3
3
1
1
3
2
1
1
2
2
2
3
3
2
1
1
2
2
1
3
2
1
1
2
3
3
3
3
2
2
2
2
2
1
3
 1
3
 2
2
1
 5
2
3
3
1
1
 5
2
2
2
2
2
 6
2
2
2
3
1
3
 5
2
3
3
3
3
 1
2
 100
2
2
1
3
1
3
3
1
1
3
1
1
3
2
1
3
1
1
3
3
2
2
3
1
1
2
3
2
2
3
1
1
2
3
2
1
2
2
3
3
1
1
3
1
2
1
3
1
1
3
2
2
2
1
1
1
3
1
3
2
1
2
2
2
3
3
2
1
1
3
3
2
1
2
1
1
3
1
2
3
2
3
3
3
2
2
1
3
1
2
3
1
2
3
3
1
2
1
3
1
 4
1
2
2
1
 3
3
3
1
 8
1
1
1
1
1
1
1
1
 5
1
1
1
1
3
 3
2
2
3
 3
2
2
2
 2
2
2
 4
2
3
3
3
 2
3
2
 100
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
 7
2
2
2
2
2
2
2
 3
2
1
1
 10
2
3
3
3
3
2
2
2
3
2
 3
3
1
3
 2
3
1
 3
1
2
3
 42
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
 2
1
3
 100
2
3
1
2
3
3
3
1
1
1
1
3
3
3
3
1
2
3
3
3
3
3
3
3
1
2
2
2
3
1
1
3
3
3
3
3
3
3
3
1
2
3
3
3
1
1
1
1
3
3
3
3
1
2
3
1
2
2
2
3
3
2
1
3
3
1
2
3
1
1
1
2
2
2
3
1
1
1
1
1
1
3
2
2
2
2
2
2
3
1
2
2
2
2
2
3
3
2
1
1
 3
3
2
2
 3
3
2
3
 2
3
3
 3
2
2
1
 5
1
1
2
2
3
 3
1
3
1
 3
1
1
3

YES
 NO
 NO
 NO
 YES
 NO
 YES
 YES
 NO
 NO
 NO
 YES
 NO
 NO
 YES
 YES
 YES
 NO
 YES
 YES
 NO
 NO
 NO
 NO
 NO
 YES
 YES
 YES
 NO
 NO
 NO
 YES
 NO
 NO
 NO

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Calendar;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Scanner;
import java.util.Stack;

public class Main {


	private static Scanner in = new Scanner(System.in);
	 

	public static void main(String[] args) {
		
	
		int n = in.nextInt();
	
		int [] a = new int[n];
		
		for(int i = 0;i<n;i++) {
			a[i]=in.nextInt();			
		}
			
		int [] b = new int[n];
		
		b[0]=3;

		boolean flag = false;
		
		for (int i = 1; i < b.length; i++) {
			b[i]=6-a[i-1]-b[i-1];
			if(a[i]==b[i])  {
				flag = true;
				System.out.println("NO");
				break;
			}	
		}	if(!flag) System.out.println("YES");		
		
		
	} static void fillAnArray(int [] a) {
		for (int i = 0; i < a.length; i++) {
			a[i]=in.nextInt();
		}
	}
	static int sumOfArray(int [] a) {
		int sum = 0;
		for (int i = 0; i < a.length; i++) 
			if(a[i]>0)sum+=a[i];			
		return sum;
	}
	static int numberOfElementsAboveZero(int [] a) {
		int num = 0;
		for (int i = 0; i < a.length; i++) {
			if(a[i]>0) num++;
		}		
		return num;
	}
	static int min(int [] a) {
		int min = Integer.MAX_VALUE;
		for (int i = 0; i < a.length; i++) {
			if(a[i]>0 && a[i]<min) {
				min=a[i];
			}
		}
		return min;
	}
	static void dis(int [] a ,int min) {
		for (int i = 0; i < a.length; i++) {
			a[i]-=min;
		}
	}
	static boolean isPrime(int n) {
		
		if(n < 2) return false;
		
		for (int i = 2; i <= (int)Math.sqrt(n); i++) 
			if(n%i==0) return false;
			return true;
		
	}

}
