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: Runtime Error)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            // スペース区切りの整数の入力
            long[] D = Console.ReadLine().Split().Select(long.Parse).ToArray();

            long N, a, b, l, out1;
            N = D[0];
            b = D[1];
            a = N - b;
            l = Math.Abs(N - b);

            out1 = N;

            while (l != 0)
            {
                if (a > b)
                {
                    if (b == 1)
                    {
                        out1 = out1 + 2* (a - 1);
                        break;
                    }
                    else
                    {
                        a = a - b;
                        out1 = out1 + 2 * b;
                    }
                }
                else if(a < b)
                {
                    if (a == 1)
                    {
                        out1 = out1 + 2 * (b - 1);
                        break;
                    }
                    else
                    {
                        b = b - a;
                        out1 = out1 + 2 * a;
                    }
                }
                l = Math.Abs(b - a);
            }
            if (a == 1 || b == 1)
            {
                out1 = out1 + 1;
            }
            else
            {
                out1 = out1 + a;
            }
            Console.WriteLine(out1);
        }
    }
}