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 ;
namespace Main{
 class Program{
  static void Main(string[] args){
   int N = 2 * int.Parse(Console.ReadLine());
    string []buff = Console.ReadLine().Split(' ');
    int []a = new int[N];
    for ( int i= 0 ; i< N  ;i++)
      a[i] = int.Parse(buff[i]);
    
    for ( int i = 0 ; i < N -1  ; i++){
      for ( int j = i+1 ; j < N ;j++){
        if( a[i] > a[j]){
         int swap = a[i];
          a[i] = a[j];
          a[j] = swap;
        }
      }
    }
    int sum = 0;
    for ( int i = 0 ; i < N / 2  ;i++){
      sum += min(a[2 * i],a[2 * i+1]); 
    }
    Console.WriteLine(sum);
  }
   static int min(int a , int b){
    return a < b ? a : b  ;
   }
 }
}