#include <bits/stdc++.h>
using namespace std;
long long N, A[100];
int main(void) {
  cin >> N;
  for (long long i = ((long long)0); i < ((long long)N); i++) cin >> A[i];
  bool ans = true;
  long long p1 = 1, p2 = 2, s = 3;
  for (long long i = ((long long)0); i < ((long long)N); i++) {
    if (A[i] == p1) {
      swap(p2, s);
    } else if (A[i] == p2) {
      swap(p1, s);
    } else {
      ans = false;
      break;
    }
  }
  cout << (ans ? "YES" : "NO") << endl;
}
