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.*;
import java.lang.reflect.Array;
import java.util.*;
import java.util.stream.Stream;

public class Main {
    public static long Nod(long a, long b)
    {
        while (a != 0 && b != 0)
            if (a >= b)
                a %= b;
            else
                b %= a;
        return a | b;
    }

    public static void main(String[] args) throws IOException {
        FastScanner in = new FastScanner(/*new InputStreamReader(new FileInputStream(new File("dijkstra.in")))); */ System.in);
        FastPrinter out = new FastPrinter(/*new OutputStreamWriter(new FileOutputStream(new File("dijkstra.out")))); */  System.out);
        int n = in.nextInt();
        int k1 = 1, k2 = 2;
        boolean flag = true;
        for(int i = 0; i < n; i++){
            int a = in.nextInt();
            if (a != k1 && a != k2){
                System.out.println("NO");
                flag = false;
                break;
            }
            if(a == k1){
                k2 = 6 - a - k2;
            }
            if(a == k2){
                k1 = 6 - a - k1;
            }
        }
        if(flag)
        out.println("YES");
        out.close();
    }
}

class FastPrinter {
    private final PrintWriter writer;

    public FastPrinter(OutputStream outputStream) {
        writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
    }

    public FastPrinter(Writer writer) {
        this.writer = new PrintWriter(writer);
    }

    public void close() {
        writer.close();
    }

    public void println(long i) {
        writer.println(i);
    }

    public void println(double d) {
        writer.println(d);
    }

    public void println(String s) {
        writer.println(s);
    }

    public void println(String format, Object... args) {
        println(String.format(format, args));
    }

    public void println() {
        writer.println();
    }

    public void print(long i) {
        writer.print(i);
    }

    public void print(char c) {
        writer.print(c);
    }

    public void print(double d) {
        writer.print(d);
    }

    public void print(String s) {
        writer.print(s);
    }

    public void print(String format, Object... args) {
        print(String.format(format, args));
    }

    public void flush() {
        writer.flush();
    }
}

class FastScanner {

    private BufferedReader reader;
    private StringTokenizer st;
    private byte[] buf = new byte[1024];
    private int curChar;
    private int numChars;
    private SpaceCharFilter filter;

    public FastScanner(InputStream stream) {
        this.reader = new BufferedReader(new InputStreamReader(stream));
        this.st = new StringTokenizer("");
    }

    public FastScanner(InputStreamReader stream) {
        this.reader = new BufferedReader(stream);
        this.st = new StringTokenizer("");
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }

    public long nextLong() {
        return Long.parseLong(next());
    }

    public double nextDouble() {
        return Double.parseDouble(next());
    }

    public String next() {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(readLine());
        }
        return st.nextToken();
    }

    public String nextLine() {
        st = new StringTokenizer("");
        return readLine();
    }

    public String tryNextLine() {
        st = new StringTokenizer("");
        return tryReadLine();
    }

    private String readLine() {
        String line = tryReadLine();
        if (line == null) throw new InputMismatchException();
        return line;
    }

    private String tryReadLine() {
        try {
            return reader.readLine();
        } catch (IOException e) {
            throw new InputMismatchException();
        }
    }

    public int[] nextIntArray(int size) {
        int[] array = new int[size];
        for (int i = 0; i < size; i++)
            array[i] = nextInt();
        return array;
    }

    public int[][] nextIntTable(int rowCount, int columnCount) {
        int[][] table = new int[rowCount][];
        for (int i = 0; i < rowCount; i++)
            table[i] = nextIntArray(columnCount);
        return table;
    }

    public long[] nextLongArray(int size) {
        long[] array = new long[size];
        for (int i = 0; i < size; i++)
            array[i] = nextLong();
        return array;
    }

    public long[][] nextLongTable(int rowCount, int columnCount) {
        long[][] table = new long[rowCount][];
        for (int i = 0; i < rowCount; i++)
            table[i] = nextLongArray(columnCount);
        return table;
    }

    public boolean isSpaceChar(int c) {
        if (filter != null)
            return filter.isSpaceChar(c);
        return isWhitespace(c);
    }

    public static boolean isWhitespace(int c) {
        return c == ' ' || c == '\t' || isEOL(c);
    }

    public static boolean isEOL(int c) {
        return c == '\n' || c == '\r' || c == -1;
    }

    public interface SpaceCharFilter {
        public boolean isSpaceChar(int ch);
    }
}
