#include <bits/stdc++.h>
using namespace std;
void setprime(bool isprime[], long long n);
long long BinarySearch(long long arr[], long long first, long long last,
                       long long search);
long long choose(long long n, long long k);
void showArray(long long a[], long long n);
long long gcd(long long a, long long b);
long double len(long double x1, long double y1, long double x2, long double y2);
long double gcd_ld(long double x, long double y);
long long power(long long x, long long n);
int main() {
  cin.tie(0);
  cout.tie(0);
  ios::sync_with_stdio(0);
  cout << fixed;
  cout << setprecision(6);
  long long n;
  cin >> n;
  long long a[n];
  for (long long i = 0; i < n; i++) cin >> a[i];
  if (a[0] == 3) {
    cout << "NO";
    return 0;
  }
  long long cp1 = 1, cp2 = 2, sp = 3;
  for (long long i = 0; i < n; i++) {
    if (a[i] == cp1 || a[i] == cp2) {
      if (a[i] == cp1) {
        long long tmp = sp;
        sp = cp2;
        cp2 = tmp;
      } else {
        long long tmp = sp;
        sp = cp1;
        cp1 = tmp;
      }
    } else {
      cout << "NO";
      return 0;
    }
  }
  cout << "YES";
  return 0;
}
void setprime(bool isprime[], long long n) {
  for (long long i = 0; i < n; i++) isprime[i] = true;
  isprime[0] = false;
  isprime[1] = false;
  for (long long i = 2; i < n; i++) {
    for (long long j = 2; i * j < n; j++) isprime[i * j] = false;
  }
}
long long BinarySearch(long long arr[], long long first, long long last,
                       long long search) {
  long long middle = (first + last) / 2;
  while (first <= last) {
    if (arr[middle] < search) {
      first = middle + 1;
    } else if (arr[middle] == search) {
      return middle;
    } else {
      last = middle - 1;
    }
    middle = (first + last) / 2;
  }
  if (first > last) {
    return -1;
  }
}
long long choose(long long n, long long k) {
  if (k == 0) return 1;
  return (n * choose(n - 1, k - 1)) / k;
}
void showArray(long long a[], long long n) {
  for (long long i = 0; i < n; i++) {
    cout << a[i] << " ";
  }
  cout << endl;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long double len(long double x1, long double y1, long double x2,
                long double y2) {
  return sqrt(pow((x1 - x2), 2) + pow((y1 - y2), 2));
}
long double gcd_ld(long double x, long double y) {
  long double eps = 0.0001;
  while (fabs(x) > eps && fabs(y) > eps) {
    if (x > y)
      x -= floor(x / y) * y;
    else
      y -= floor(y / x) * x;
  }
  return x + y;
}
long long power(long long x, long long n) {
  if (n == 0)
    return 1;
  else if (n % 2 == 0)
    return power(x * x, n / 2);
  else
    return x * power(x * x, (n - 1) / 2);
}
