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: Accepted)

#include <stdio.h>

int N;
void swap(int *n1, int *n2){int tmp = *n1; *n1 = *n2; *n2 = tmp;}
void sort(int array[]);

int main(void)
{
	int i, L[210], ans = 0;
	scanf("%d", &N);
	for (i = 0; i < 2 * N; i++){
		scanf("%d", &L[i]);
	}

	sort(L);

	for (i = 0; i < 2 * N; i += 2){
		ans += L[i];
	}
	printf("%d\n", ans);

	return 0;
}

void sort(int array[])
{
	int i, j;
	for (i = 2 * N - 1; i > 0; i--){
		for (j = 0; j < i; j++){
			if (array[j] > array[j + 1])
				swap(&array[j], &array[j + 1]);
		}
	}
}