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>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#include <math.h>

#define MOD 1000000007
#define REP(i,n) for ((i)=0;i<(n);i++)
#define SET(a,c) memset(a,c,sizeof a)
#define CLR(a) memset(a,0,sizeof a)
#define MIN(a,b) (a>b?b:a)
#define MAX(a,b) (a>b?a:b)
#define LL long long
#define ULL unsigned long long


int compare_int(const void *a, const void *b)
{
    return *(int*)a - *(int*)b;
}

int main(void) {

	int N,L[100],i;
	long ans=0;
	scanf("%d",&N);
	REP(i,N*2)	scanf("%d", &L[i]);
	qsort(L,N*2,sizeof(int),compare_int);
	REP(i,N)	ans +=L[i*2];

	printf("%ld\n", ans);
	return 0;
}

/* 最後の改行忘れるな！！ */