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: Accepted)

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

public class Main {
	public static void main(String[] args) throws IOException {
		new Main().run();
		
	}
	
	private static void run() throws IOException {
		BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
		
		int N = Integer.parseInt(reader.readLine());
		int[] list = new int[2 * N];
		int sum = 0;
		
		String str = reader.readLine();
		int index1 = -1;
		int index2 = -1;
		
		for (int i = 0; i < 2 * N; ++i) {
			index2 = str.indexOf(" ", index1 + 1);
			if (index2 == -1) {
				index2 = str.length();
			}
			
			list[i] = Integer.parseInt(str.substring(index1 + 1, index2));
			// System.out.println(list[i]);
			
			index1 = index2;
			
		}
		
		Arrays.sort(list);
		
		for (int i = 0; i < 2 * N; i += 2) {
			sum += list[i];
			
		}
		
		System.out.println(sum);
		
	}
}