#include<bits/stdc++.h>
using namespace std;

int n,a[100004],t1,t2,t3,t4,res;

int main()
{
	cin>>n;
	for(int i=1;i<=n;++i)
	{
		cin>>a[i];
		if(a[i]==1) t1++;
		if(a[i]==2) t2++;
		if(a[i]==3) t3++;
		if(a[i]==4) t4++;
	}

	res=t4;
	if(t2%2==0) res+=t2/2;
	else
	{
		res+=t2/2+1;
		t1-=2;
	}
	if(t1>0)
	{
		res+=t3;
		t1-=t3;
	}
	else
	{
		cout<<res+t3;
		return 0;
	}
	if(t1>0)
	{
		if(t1%4==0) res+=t1/4;
			else res+=t1/4+1;
	}
	cout<<res;
}