#include<bits/stdc++.h>
using namespace std;
int main()
{
    int t,n,ck=0,count=0;
    double arr[5]={0};
    double sum=0;

    cin >> t;

    while(t--)
    {
        cin >> n;
        arr[n]++;
    }

    count = min(arr[1],arr[3]);
    arr[1] = arr[1] - count;
    arr[3] = arr[3] - count;
    count = count + arr[4] + arr[3];
    count = count + ceil((arr[1]+2*arr[2])/4.0) ;
    cout<<count;
    return 0;
}