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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.InputMismatchException;
				
					 
					public class Solution1 implements Runnable
					{
						static final int MAX = 1000000007;
						static class InputReader
						{
							private InputStream stream;
							private byte[] buf = new byte[1024];
							private int curChar;
							private int numChars;
							private SpaceCharFilter filter;
							private BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
					
							public InputReader(InputStream stream)
							{
								this.stream = stream;
							}
							
							public int read()
							{
								if (numChars==-1) 
									throw new InputMismatchException();
								
								if (curChar >= numChars)
								{
									curChar = 0;
									try 
									{
										numChars = stream.read(buf);
									}
									catch (IOException e)
									{
										throw new InputMismatchException();
									}
									
									if(numChars <= 0)				
										return -1;
								}
								return buf[curChar++];
							}
						 
							public String nextLine()
							{
								String str = "";
					            try
					            {
					                str = br.readLine();
					            }
					            catch (IOException e)
					            {
					                e.printStackTrace();
					            }
					            return str;
							}
							public int nextInt()
							{
								int c = read();
								
								while(isSpaceChar(c)) 
									c = read();
								
								int sgn = 1;
								
								if (c == '-') 
								{
									sgn = -1;
									c = read();
								}
								
								int res = 0;
								do 
								{
									if(c<'0'||c>'9') 
										throw new InputMismatchException();
									res *= 10;
									res += c - '0';
									c = read();
								}
								while (!isSpaceChar(c)); 
								
								return res * sgn;
							}
							
							public long nextLong() 
							{
								int c = read();
								while (isSpaceChar(c))
									c = read();
								int sgn = 1;
								if (c == '-') 
								{
									sgn = -1;
									c = read();
								}
								long res = 0;
								
								do 
								{
									if (c < '0' || c > '9')
										throw new InputMismatchException();
									res *= 10;
									res += c - '0';
									c = read();
								}
								while (!isSpaceChar(c));
									return res * sgn;
							}
							
							public double nextDouble() 
							{
								int c = read();
								while (isSpaceChar(c))
									c = read();
								int sgn = 1;
								if (c == '-') 
								{
									sgn = -1;
									c = read();
								}
								double res = 0;
								while (!isSpaceChar(c) && c != '.') 
								{
									if (c == 'e' || c == 'E')
										return res * Math.pow(10, nextInt());
									if (c < '0' || c > '9')
										throw new InputMismatchException();
									res *= 10;
									res += c - '0';
									c = read();
								}
								if (c == '.') 
								{
									c = read();
									double m = 1;
									while (!isSpaceChar(c)) 
									{
										if (c == 'e' || c == 'E')
											return res * Math.pow(10, nextInt());
										if (c < '0' || c > '9')
											throw new InputMismatchException();
										m /= 10;
										res += (c - '0') * m;
										c = read();
									}
								}
								return res * sgn;
							}
							
							public String readString() 
							{
								int c = read();
								while (isSpaceChar(c))
									c = read();
								StringBuilder res = new StringBuilder();
								do 
								{
									res.appendCodePoint(c);
									c = read();
								} 
								while (!isSpaceChar(c));
								
								return res.toString();
							}
						 
							public boolean isSpaceChar(int c) 
							{
								if (filter != null)
									return filter.isSpaceChar(c);
								return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
							}
						 
							public String next() 
							{
								return readString();
							}
							
							public interface SpaceCharFilter 
							{
								public boolean isSpaceChar(int ch);
							}
						}
					 	
						public static void main(String args[]) throws Exception
						{
							new Thread(null, new Solution1(),"Solution1",1<<26).start();
						}
						long power(long x, long y)
						{
						    long res = 1;      // Initialize result
						 
						    x = x % MAX;  // Update x if it is more than or 
						                // equal to p
						 
						    while (y > 0)
						    {
						        // If y is odd, multiply x with result
						        if (y % 2 == 1)
						            res = (res*x) % MAX;
						 
						        // y must be even now
						        y = y>>1; // y = y/2
						        x = (x*x) % MAX;  
						    }
						    return res;
						}
						public void run()
						{
							InputReader sc= new InputReader(System.in);
							PrintWriter w= 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 one = 1;
							int two = 2;
							int three = 3;
							for(int i = 0;i < n;i++){
								if(arr[i] != one && arr[i] != two){
									w.print("NO");
									w.close();
									System.exit(0);
								}else{
									if(arr[i] == one){
										int tmep = two;
										two = three;
										three=   tmep;
									}else{
										int tmep = one;
										one = three;
										three = tmep;
									}
								}
							}
							w.println("YES");
							w.close();
						}
						public static int gcd(int a, int b)
					    {
					        if (a == 0)
					            return b;
					         
					        return gcd(b%a, a);
					    }
						static class Pair implements Comparable<Pair>{
							int a;
							int b;
							Pair(int a,int b)	{
								this.a = a;
								this.b = b;
							}
							public boolean equals(Object o)
							{
								Pair p = (Pair)o;
								return p.a==a && p.b==b;
							}
							public int compareTo(Pair p){
								return Long.compare(this.a,p.a);
							}
							public int hashCode()
							{
								return new Long(a).hashCode()*31 + new Long(a).hashCode();
							}
						}
					}