#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
using namespace std;
int f[40000][4],f2[40000][4],n,a[40000];
int dp()
{
   for (int i=1;i<=n;i++)
   for (int j=1;j<=3;j++)
    f[i][j]=i;
//初始化
  for (int i=1;i<=n;i++)
  {
    for (int j=1;j<=3;j++)
    for (int k=1;k<=j;k++)
//枚举上一次是哪种状态，且这种状态必须小于等于j
//如果相等的话直接更新就行
    if (a[i]==j) f[i][j]=min(f[i][j],f[i-1][k]);
//否则还要更改当前的这个
    else f[i][j]=min(f[i][j],f[i-1][k]+1);
  }
  return (min(min(f[n][1],f[n][2]),f[n][3]));
}
int main()
{
  scanf("%d",&n);
  for (int i=1;i<=n;i++) scanf("%d",&a[i]);
  int ans=dp();
//正着来一遍，反着来一遍
  for (int i=1;i<=n/2;i++) {int t=a[i];a[i]=a[n-i+1];a[n-i+1]=t;}
  ans=min(ans,dp());
  printf("%d\n",ans);
  return 0;
}