codeforces 158b taix （水题贪心）

B. Taxi

time limit per test

3 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

After the lessons n groups of schoolchildren went outside and decided to visit Polycarpus to celebrate his birthday. We know that the i-th group consists of si friends (1 ≤ si ≤ 4), and they want to go to Polycarpus together. They decided to get there by taxi. Each car can carry at most four passengers. What minimum number of cars will the children need if all members of each group should ride in the same taxi (but one taxi can take more than one group)?

Input

The first line contains integer n (1 ≤ n ≤ 105) — the number of groups of schoolchildren. The second line contains a sequence of integers s1, s2, ..., sn (1 ≤ si ≤ 4). The integers are separated by a space, si is the number of children in the i-th group.

Output

Print the single number — the minimum number of taxis necessary to drive all children to Polycarpus.

Examples

input

Copy

5
1 2 4 3 3

output

Copy

4

input

Copy

8
2 3 4 4 2 1 3 1

output

Copy

5

Note

/*主要思路为，尽量先让接近4的人上车，如果不够4个
让人数少的来拼车凑*/ 
#include <iostream>
#include <string.h>
#include <algorithm>
using namespace std;
int a[100005];
int main()
{
	int n,i,sum,j,flag,ans;
	while(cin>>n)
	{
		sum=0;
		for(i=1;i<=n;i++)
		cin>>a[i];
		sort(a+1,a+n+1);
		for(i=n,j=0;i>j;i--)
		{
			if(a[i]==4)
			sum++;
			else
			{
				ans=a[i];
				while(ans<4)
				{
					ans+=a[++j];
				}
				if(ans==4)
				{
					sum++;
				}
				else
				{
					sum++;
					j--;
				}
			}
		}
		cout<<sum<<endl;
	}
	return 0;
}