#include <bits/stdc++.h>
const int mod = 1e9 + 7;
const double eps = 1e-6;
const double pi = acos(-1);
const int inf = 0x7fffffff;
using namespace std;
int a[105];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
  if (a[1] == 3) return 0 * printf("NO\n");
  int x = 1, y = 2;
  for (int i = 1; i <= n; i++) {
    if (a[i] == x) {
      if (x == 1) {
        if (y == 2)
          y = 3;
        else
          y = 2;
      } else if (x == 2) {
        if (y == 1)
          y = 3;
        else
          y = 1;
      } else if (x == 3) {
        if (y == 1)
          y = 2;
        else
          y = 1;
      }
    } else if (a[i] == y) {
      if (y == 1) {
        if (x == 2)
          x = 3;
        else
          x = 2;
      } else if (y == 2) {
        if (x == 1)
          x = 3;
        else
          x = 1;
      } else if (y == 3) {
        if (x == 1)
          x = 2;
        else
          x = 1;
      }
    } else
      return 0 * printf("NO\n");
  }
  printf("YES\n");
  return 0;
}
