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 JavaScript (node.js v5.12) (judge verdict: Time Limit Exceeded)

function gcd(a, b) {
	while (true) {
		if (a > b) {
			a = a % b;
			if (a === 0) return b;
		} else {
			b = b % a;
			if (b === 0) return a;
		}
	}
}

function Main(input) {
const lines = input.split('\n');
const NS = lines[0].split(' ');
const N = Number(NS[0]);
const S = Number(NS[1]);
 
console.log(3 * (N - gcd(N - S, S)));
}
 
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));