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++14 (GCC 5.4.1) (judge verdict: Accepted)

#ifdef ConanYu
#include "local.hpp"
#else
#pragma GCC optimize("-O3")
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
void Main();
#define debug(...) do { } while(0)
int main() {
  ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  Main();
}
#endif

const int N = 105;
int a[N << 1];

void Main() {
  int n; cin >> n;
  for(int i = 0; i < 2 * n; i++) {
    cin >> a[i];
  }
  sort(a, a + 2 * n);
  int ans = 0;
  for(int i = 0; i < n; i++) {
    ans += a[i * 2];
  }
  cout << ans << "\n";
}