#include <bits/stdc++.h>
using namespace std;
int main() {
  int tmp = 3;
  int x = 1, y = 2;
  int n;
  cin >> n;
  bool flag = true;
  for (int i = 1; i <= n; i++) {
    int q;
    cin >> q;
    if (q == tmp) {
      flag = false;
    }
    if (q == x)
      swap(tmp, y);
    else
      swap(tmp, x);
  }
  if (flag)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  return 0;
}
