#include <bits/stdc++.h>

using namespace std;

int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);

    int n, a, result = 0, ones = 0, twos = 0, threes = 0;
    cin >> n;

    for(int i = 0; i < n; i++){
        cin >> a;
        if(a != 4){
            if(a == 1){
                ones++;
            } else if(a == 2){
                twos++;
            } else{
                threes++;
            }
        } else{
            result++;
        }
    }

    int onethreegroups = min(ones, threes);
    result += threes;
    ones -= onethreegroups;

    int doubletwos = twos / 2;
    result += doubletwos;
    twos -= doubletwos * 2;

    if(twos == 1){
        result++;
        ones -= min(2, ones);
    }

    result += ceil((float)ones / 4);

    cout << result;

    cout << flush;

    return 0;
}