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 (GCC 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>

int main()
{
  int n;
  int l[100];
  int i,j;
  int tmp;
  int sum;
  scanf("%d",&n);
  for(i=0;i<2*n;i++)
  {
    scanf("%d",&l[i]);
  }
  for(i=0;i<2*n;i++)
  {
    for(j=i+1;j<2*n;j++)
    {
      if(l[i] < l[j])
      {
        tmp = l[i];
        l[i] = l[j];
        l[j] = tmp;
      }
    }
  }
  for(i=0;i<n;i++)
  {
    sum += l[i*2+1];
  }
  printf("%d\n",sum);
  return 0;
}