#include<iostream>
using namespace std;

int main(){
    int n;
    cin>>n;
    int arr[n];
    int ones=0;
    int threes=0;
    int twos=0;
    int sum=0;
    for(int i=0;i<n;i++){
        cin>>arr[i];
        if(arr[i]==1){
            ones++;
        }
        else if(arr[i]==3){
            threes++;
        }
        else if(arr[i]==4){
            sum++;
        }
        else if(arr[i]==2){
            twos++;
        }
    }
    int pair_of_3_1;
    if(ones!=0 && threes!=0){
    if(ones==threes){
        pair_of_3_1=ones;
    }
    else{
        if(ones>threes){
            pair_of_3_1=threes;
            ones-=threes;
        }
        else{
            pair_of_3_1=ones;
            threes-=ones;
        }
        
    }
    }
    sum+=pair_of_3_1;
    
    if(twos!=0 && twos%2==0){
        sum+=twos/2;
        twos=0;
    }
    else{
        sum+=twos/2;
        twos=1;
    }

    if(ones>0){
        if(ones>=2){
            ones-=2;
            twos=0;
            sum+=1;
            if(ones>0){
                sum=sum+ones%4 +ones/4 ;
            }
        }
    }

    else if(threes>0){
        sum+=threes;
    }
    else if(twos>0){
        sum+=1;
    }

    cout<<sum;


    
    
}