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;
public class Program{
    public static void Main(){
        int kusi = int.Parse(Console.ReadLine());
        string[] leng = Console.ReadLine().Split(' ');
        Array.Sort(leng);
        int x = 0;
        int[] len = new int[kusi*2];
        for(int i=0;i<kusi*2;i++){
            len[i] = int.Parse(leng[i]);
        }
        for(int j=0;j<kusi*2;j++){
            for(int i=0;i<kusi*2-1;i++){
                if(len[i]>len[i+1]){
                    int temp = len[i];
                    len[i] = len[i+1];
                    len[i+1] = temp;
                }
            }
        }
        for(int i=0;i<kusi;i++){
            x += len[i*2];
        }
        Console.WriteLine(x);
    }
}