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)

/*
 * 高橋君はバーベキューをしようとしています。 バーベキューでは 2 本の串にいくつかの具材を刺した串焼きを N 個作る予定です。
 * 
 * 串は 2N 本あり、i 番目の串の長さは Li です。具材は無限に用意されています。
 * 
 * 串を 2 本組にして具材を刺して串焼きにするのですが、2 本の串のうち短い方の長さを x とすると、串焼きには最大 x 個の具材を刺すことができます。
 * 
 * うまく串を組み合わせたとき、N 個の串焼きに刺すことのできる具材の個数の和の最大値はいくらになるでしょうか？
 */

import java.util.*;
	public class Main{
        public static void main(String[] args){
            Scanner sc = new Scanner(System.in);
            //入力
            int n = Integer.parseInt(sc.next());
            int[] sticks = new int[2*n];
            int ret = 0;
            
            for(int i=0; i<2*n; i++){
            	sticks[i] = Integer.parseInt(sc.next());
            }
            
            Arrays.sort(sticks);
            
            for(int i=0; i<n; i++){
            	ret += sticks[2*i];
            }
            
            //出力
            System.out.println(ret);
            sc.close();
        }
    }