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
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1
1
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3
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1
1
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1
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1
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1
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1
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1
1
1
1
1
1
1
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1
1
1
1
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1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
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1
1
1
 7
2
2
2
2
2
2
2
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2
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2
3
3
3
3
2
2
2
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2
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3
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1
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1
1
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1
1
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1
1
1
1
1
1
1
1
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1
1
1
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1
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1
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1
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1
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 2
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 100
2
3
1
2
3
3
3
1
1
1
1
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3
3
3
1
2
3
3
3
3
3
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1
2
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1
1
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3
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1
2
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1
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2
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 3
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 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

'''input
4
1 5 2 5
'''

import sys
pow2 = pow              # for modular expo pow2(base, n, mod)
from math import *
from time import time
from collections import defaultdict
from bisect import bisect_right, bisect_left
from string import ascii_lowercase as lcs
from string import ascii_uppercase as ucs
from fractions import Fraction, gcd
from decimal import Decimal, getcontext
from itertools import product, permutations, combinations
#getcontext().prec = 500
#sys.setrecursionlimit(30000)

# What doesn't challenge you, makes you weaker.

mod = 10**9 + 7
INF = sys.maxint

raw_input = lambda: sys.stdin.readline().rstrip()
die = lambda : exit(0)
flush= lambda : sys.stdout.flush()

r_s = lambda: raw_input().strip()                   #read str
r_ss = lambda: raw_input().split()          #read stringss
r_i = lambda: int(raw_input())              #read int
r_is = lambda: map(int, raw_input().split())#read ints
r_f = lambda: float(raw_input())            #read float
r_fs = lambda: map(Decimal, raw_input().split()) #read floats

# For effieciently taking lots of queries with each query in a separate line
# having integer values separated by space. A 2d list is made with each row
# corresponding to line. Each row is a list with all the values.
# Use this for fast I/O by taking all input in one go.
r_qs = lambda: map(lambda s:map(int, s.split(' ')), sys.stdin.readlines())

'''-------------------------------------------------------------------'''

# Call it as dbg(varName=varName)
def dbg(**kwargs):
    print "Value of '" + kwargs.keys()[0] + "' is", kwargs[kwargs.keys()[0]]


def main():
    n = r_i()
    # arr = r_is()
    a = [0,1,1,0]
    for i in range(n):
        k = r_i()
        # print k
        if a[k]==0:
            print "NO"
            return
        for i in range(1,4):
            if i!=k:
                if a[i]==0:
                    a[i]=1
                else:
                    a[i]=0
        # print a
    print "YES"


if __name__ == '__main__':
    local = True
    # local = False
    if local:
        try:
            sys.stdin = open('input.txt')
            print 'Running at local.'
            for i in range(r_i()):
                main()
        except IOError:
            main()
    else:
        main()


