#include<bits/stdc++.h>
using namespace std;
int main()
{
int n , a[100000] ;
cin>>n;
int tong = 0;
for (int i=1;i<=n;i++)
{
cin>>a[i];
}
sort(a+1,a+1+n);
int i=1;
tong = 0;
int dem = 0;
while (i!=n)
{
tong = tong + a[i];
if (tong>=4)
{
tong = 0;
dem++;
}
else
{i++;}
}
cout<<dem;
return 0;
}
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