#include <iostream>
#include <vector>
using namespace std;

int dp[100005][10];
int main()
{
    int n;
    cin>>n;
    vector<int>v;
    for(int i=0; i<n; i++){
        int a;
        cin>>a;
        v.push_back(a);
    }

    int result=0;
    for(int i=0; i<=n; i++){
        for(int j=0; j<=3; j++){
            dp[i][j]=-1;

        }
    }

    dp[0][0]=0;
    for(int i=0; i<n; i++){
        for(int previous_activity=0; previous_activity<=3; previous_activity++){
         if(v[i]==0){
            dp[i+1][0]=max(dp[i+1][0], dp[i][previous_activity]);
         }
         if(v[i]==1){
            if(previous_activity!=1){
                dp[i+1][1]=max(dp[i+1][1], dp[i][previous_activity]+1);
            }
         }
        dp[i+1][0]=max(dp[i+1][0], dp[i][previous_activity]);

        if(v[i]==2){
            if(previous_activity!=2){
                dp[i+1][2]=max(dp[i+1][2], dp[i][previous_activity]+1);
            }
        }
        dp[i+1][0]=max(dp[i+1][0], dp[i][previous_activity]);

         if(v[i]==3){
            if(previous_activity!=2){
                dp[i+1][2]=max(dp[i+1][2], dp[i][previous_activity]+1);
            }
            if(previous_activity!=1){
                dp[i+1][1]=max(dp[i+1][1], dp[i][previous_activity]+1);
            }
        dp[i+1][0]=max(dp[i+1][0], dp[i][previous_activity]);

         }
         }
         }

         for(int i=0; i<=n; i++){
            for(int j=0; j<=3; j++){
                result=max(result, dp[i][j]);
            }
         }

         cout<<result;


    return 0;
}