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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {

        static void Main(string[] args)
        {
            //Console.SetIn(new StreamReader("input.txt"));
            int N = In.Int();
            List<int> inputs = In.Ints().OrderBy(a => a).ToList();
            int n = 0;
            for(int i = 0; i < N; i++)
            {
                n += inputs[0];
                inputs.RemoveAt(0);
                inputs.RemoveAt(0);
            }

            Out(n);



            return;
        } 

        private static void Out(Object arg)
        {
            Console.WriteLine(arg);
        }
    }

    class In
    {
        public static int Int()
        {
            return int.Parse(Console.ReadLine());
        }

        public static IEnumerable<int> Ints()
        {
            return Console.ReadLine().Split(' ').Select(i => int.Parse(i));
        }
    }
}