Problem:
Score : 200 points

Problem Statement

Snuke is having a barbeque party.

At the party, he will make N servings of Skewer Meal.

Example of a serving of Skewer Meal

He has a stock of 2N skewers, all of which will be used in Skewer Meal. The length of the i-th skewer is L_i.
Also, he has an infinite supply of ingredients.

To make a serving of Skewer Meal, he picks 2 skewers and threads ingredients onto those skewers.
Let the length of the shorter skewer be x, then the serving can hold the maximum of x ingredients.

What is the maximum total number of ingredients that his N servings of Skewer Meal can hold, if he uses the skewers optimally?

Constraints

1≦N≦100

1≦L_i≦100

For each i, L_i is an integer.

Input

The input is given from Standard Input in the following format:

N
L_1 L_2 ... L_{2N}

Output

Print the maximum total number of ingredients that Snuke's N servings of Skewer Meal can hold.

Sample Input 1

2
1 3 1 2

Sample Output 1

3

If he makes a serving using the first and third skewers, and another using the second and fourth skewers, each serving will hold 1 and 2 ingredients, for the total of 3.

Sample Input 2

5
100 1 2 3 14 15 58 58 58 29

Sample Output 2

135

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/**
 * Hello world!
 *
 */
public class Main {
	public static void main(String[] args) {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
		int first = Integer.parseInt(br.readLine());
		int result = 0;

		String[] arr;
			arr = br.readLine().split(" ");
		List<String> second = new ArrayList<String>();
		second.addAll(Arrays.asList(arr));
		for (int i = 0; i < first; i++) {
			int a = Integer.parseInt(second.get(0));
			int data = 5000000;
			int num = 1;

			for (int j = 1; j < second.size(); j++) {
				if (data > Integer.parseInt(second.get(j)) - a && Integer.parseInt(second.get(j))-a >= 0) {
					data = Integer.parseInt(second.get(j)) - a;
					num = j;
				} else if (data > a - Integer.parseInt(second.get(j)) && a - Integer.parseInt(second.get(j)) >= 0) {
					data = a - Integer.parseInt(second.get(j));
					num = j;
				}
			}
			if (a < Integer.parseInt(second.get(num))) {
				result = result + a;
			} else {
				result = result + Integer.parseInt(second.get(num));
			}

			second.remove(num);
			second.remove(0);

		}
		System.out.println(result);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}