#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a = 1;
  int b = 2;
  bool ok = true;
  int k;
  for (int i = 0; i < n; i++) {
    cin >> k;
    if (k != a && k != b) {
      ok = false;
    } else {
      if (b == 3 && a == 1) {
        a = min(2, k);
        b = max(2, k);
      } else if (b == 2 && a == 1) {
        a = min(3, k);
        b = max(3, k);
      } else if (b == 3 && a == 2) {
        a = min(1, k);
        b = max(1, k);
      }
    }
  }
  if (ok) {
    cout << "YES";
  } else {
    cout << "NO";
  }
  return 0;
}
