TAXI686 C++

#include <bits/stdc++.h>
using namespace std;
int n,s,x,d[5];

void nhap()
{
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>x;
        d[x]++;
    }
}

void giai()
{
    s=0;
    s=d[4];
    s=s+d[3];
    d[1]=d[1]-d[3];
    s=s+(d[2]/2);
    if(d[2]%2 == 1)
    {
        s++;
        d[1]=d[1]-2;
    }
    if(d[1]>0) s=s+((d[1]-1)/4)+1;
    cout<<s;
}


int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    freopen("taxi686.inp","r",stdin);
    freopen("taxi686.out","w",stdout);
    nhap();
    giai();


}