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 Rust (1.15.1) (judge verdict: Accepted)

use std::fmt::Debug;
use std::str::FromStr;
use std::io::*;
use std::cmp::*;

fn main() {
    let i = stdin();
    solve(&mut i.lock(), &mut stdout());
}

fn solve(i: &mut BufRead, o: &mut Write) {
    let n = read::<usize>(i);
    let mut l = read_vec::<usize>(i);
    l.sort();
    let mut s = 0;
    for i in 0..n {
        s += min(l[2 * i], l[2 * i + 1]);
    }

    writeln!(o, "{}", s).unwrap();
}

fn read_line(i: &mut BufRead) -> String {
    let mut line = String::new();
    i.read_line(&mut line).unwrap();
    line.trim().to_string()
}
fn read<T: FromStr>(i: &mut BufRead) -> T
where
    T::Err: Debug,
{
    read_line(i).parse().unwrap()
}
fn read_vec<T: FromStr>(i: &mut BufRead) -> Vec<T>
where
    T::Err: Debug,
{
    read_line(i)
        .split(' ')
        .map(|x| x.parse().unwrap())
        .collect()
}