#include <iostream>
using namespace std;
int mins(int yi,int er){
    return yi<er? yi:er;
}
int main()
{
    int n,a[30001]={0};
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i];
    }
    int f[30001][4]={0};
    for(int i=1;i<=n;i++){
        for(int j=1;j<=3;j++){
            if(j>i){
                for(int k=j;k<=3;k++){
                    f[i][k]=f[i][j-1];
                }
                break;
            }
            bool bian=0;
            if(a[i]!=j){
                bian=1;
            }
            int last=j-1;
            if(j-1<1) last=j;
            int last2=j-2;
            if(j-2<1) last2=j;
            f[i][j]=mins(f[i-1][last]+bian,f[i-1][j]+bian);
            f[i][j]=mins(f[i-1][last2]+bian,f[i][j]);
            // cout<<f[i][j]<<" ";
        }
        // cout<<endl;
    }
    int ans=mins(mins(f[n][1],f[n][2]),f[n][3]);
    int h[30001][4]={0};
    for(int i=1;i<=n;i++){
        // cout<<endl;
        for(int j=3;j>=1;j--){
            if(3-j+1>i){
                for(int k=j;k>=1;k--){
                    h[i][k]=h[i][j-1];
                }
                break;
            }
            bool bian=0;
            if(a[i]!=j){
                bian=1;
            }
            int last=j+1;
            if(j+1>3) last=j;
            int last2=j+2;
            if(j+2>3) last2=j;
            h[i][j]=mins(h[i-1][last]+bian,h[i-1][j]+bian);
            h[i][j]=mins(h[i-1][last2]+bian,h[i][j]);
            // cout<<h[i][j]<<" ";
        }
    }
    cout<<mins(mins(h[n][2],h[n][3]),mins(ans,h[n][1]));
}