Coderforces Taxi

http://codeforces.com/problemset/problem/158/B

import java.util.Scanner;

public class Taxi {

	
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int n = scanner.nextInt();
		int[] a = new int[5];
		int num = 0;
		for(int i = 1; i < n+1; i++) {
			int j = scanner.nextInt();
			a[j] = a[j] + 1;
		}
		num += a[4];
		num += a[3];
		num += a[2]/2;
		if(a[2] % 2 != 0) {
			num++;
			a[2] = 1;
		} else a[2] = 0;
		if(a[1] <= a[2] * 2 + a[3]) System.out.println(num);
		else {
			int temp = a[1] - (a[2] * 2 + a[3]);
			num += (temp % 4 > 0 ? 1 : 0) + temp /4;
			System.out.println(num);
		}
	}
}